Hi Bailes. Remember you are not alone.
My wife and I moved to Fort Smith, Arkansas USA, in 2015. We have two children (they were 2 months and 24 months old at the move). My wife's parents moved from Virginia to the same town, in their own home, to be close to my wife. My mother-in-law passed away February 2017. My father-in-law (Ed) was, for the first time, living alone. He was 80 years old at the time, with moderate Parkinson's. In July 2017, my wife, kids and I moved an hour north to a new town and purchased our "forever" home. Ed ended up moving in with us in our new home. He would have otherwise been alone in a town where he had no friends. And with my wife's loss of her mother, she dearly needed to be close to her father. Not in a dysfunctional way; she has always had a great relationship with her parents. In our new home, Ed has his own bedroom upstairs in secluded wing all by itself. He has his own full bathroom, living area, and I furnished it with a complete entertainment system, computer, etc. He wanted cable, so I purchased that. He didn't shop or cook, or clean. My wife and I did all of those (my wife and I split all "domestic chores"--it is very important to us for our children to understand house work is not the "wife's" job). He does do yard work, like raking, and does take trash and recycling out; he does what he can. Plus, family is the most important thing in this world. I believe that, still. Our children will understand it, and my wife and I felt this was a good way to instill into our children the commitment we all have to family. However, that commitment doesn't mean you let family take advantage of you. It also doesn't mean you always do what the other person wants.

Ed has become more demented. Having Ed live with us interferes with our marriage. His growing confusion causes problems weekly. One time he cut all the hydrangeas in our garden; he swore my wife told him to. She had asked him to water them. This is classic for dementia; the person is 1 or 2 degrees of freedom off the mark. Ed also didn't contribute financially, at first. And, he increasingly voiced his expectations of my wife to cook his meals, clean his room, etc. Now, I admit I am old-fashioned in some ways. But no one speaks to my wife like that. So, I called him out in a loving but stern manner. I knew we had to get a hold of these reins before it was too late. Our intra-family relationships depended on it.

Here are my lessons learned (and I'm still learning). These are not in any specific order:
1. Find out how much it costs to rent a bedroom with full bath in your city/state/region. This is very important. You need to make sure you have the in-law pay this amount to you each month (it can be paid monthly, or lump sum yearly) but it must be paid. Do not "discount" it. If you do, and the in-law needs government services (for a home nurse to visit, for example) they will lose a significant amount of aid they are otherwise entitled to. If you charge them more than the going rate is, the same thing can happen, they can lose aid. So, make sure it's accurate.
2. Make sure they pay their share. They are already saving hundreds, if not thousands of dollars a month by living in your home. If they insist in having cable television, and no one else uses it, they should pay for it all. If they eat your food, they should pitch in with money. They may try instead to pitch in by going to the store or doing chores around the home. If they don't have the money to pay, then this may be a good way to help them feel as if they aren't completely dependent on you; you still want them to maintain dignity. But, sometimes (especially with dementia) people can be very possessive of everything--food, money, watching their shows on tv--if they have the money, they need to pay.
3. Ed is my wife's father. But, he is also my father-in-law. Just because he is her father, that doesn't mean that every issue I have with him must be dealt with by her. I can share my concern or frustration with her, but I need to go directly to Ed to discuss it and work it out. Likewise, if Ed is upset with me, he needs to come directly to me and not complain behind my back to my wife and expect her to fix it.
4. Our children are the number 1 priority in this house and in our lives. Period. If anyone gets in the way of our children's welfare, and they are not able to remedy their interference, they will have to leave. And that is the way it is.
5. Having in-laws live with you will be a strain on your marriage, especially if you have been married less than 10 years. Those first 10 years are rough and tough, at times. All couples have arguments. Then, they come to each other and work it out. That is how marriage gets stronger. If an in-law is living with you, it is easy for the son/daughter-in-law to think their spouse is "going to their mommy/daddy" to seek comfort, instead of coming to their spouse. Likewise, the son/daughter might suspect their spouse of harboring these sentiments. It just interferes in so many ways. Of course, you want to include the in-law/parent. But, those boundaries can become blurred. Here's what you do: in front of your parent, tell your spouse that your marriage is priority, along with the kids. Tell your spouse from time to time that you chose them, you married them, and they are your rock. They need this. If they don't hear it, they will worry where they stand.
6. You need to speak to an attorney to figure out what you need to do if/when the elder parent becomes incapacitated/unable to make decisions, pay bills, etc. At the very least, the son/daughter must be able to access all accounts (bank, checking, savings, mutual funds, stocks, retirement--everything) as well as be able to sign checks. Get all logins for their email, online banking accounts, etc. Power of attorney is a must. If you wait until they are incapacitated to start this, it will take months. MONTHS!!!
7. Talk to your children about their grandparent. Ask if they have concerns. If dementia is present, you need to ask the hard questions, too. Like, "does grandad ever tell at you? Hit you? Threaten you?". It's viscerally nauseating to think about, but it happens. Your kids need to know why grandad is there (you take care of family) but they also need to know that they are #1 on your list and in your heart, and personally I think the kids need to know their voice matters.
8. Talk to the in-law/parent, as well! Make sure they know their voice matters, and that while they may not be #1 over a young child, they are #2 and they are loved. You don't want the elder to feel like they are a "problem" or that they just get in the way. They can contribute in many ways. They may be able to baby sit (not if there is dementia). They can help with things around the house. Just ask them. They matter. Remember, they have a lifetime of experience and wisdom from all they have seen and done. Take the time to sit down and just listen.
9. Always have a plan. The day is going to come where the in-law needs to have in-home help from a nurse, or even needs to move to a living center. Does the in-law have money for this? Do they have a supplemental insurance policy to pay for it? Most don't. If they do, understand the policy usually only pays out around $100-$200 dollars monthly, for no more than 3 years typically. That money can go bye-bye really fast, but it also isn't a lump sum. So, get all of their insurance policies together and understand them. You must talk to them about their wishes. If their wishes aren't feasible or reasonable, they must be told that. They have to make a decision, or someone else will make it for them.

I would caution anyone from quickly letting their in-laws or parents move in with them. It is going to benefit them significantly. It will not benefit you. You need to understand that right now. "Oh, but they can babysit the kids. They can help pay for food, utilities, blah blah". Wrong. First, if you need them to move in to help pay the bills, you have financial problems and you need to get those in order. Having family move in isn't a fix. It's a bandaid and will only allow the continued irresponsible spending. Second, you should never commit to parents moving in simply for child care. Family is important beyond anythjng. But so are you as an individual and as a married couple and parents is important.

Instead of them moving in, it may be better to help them explore other options. Take them around to some assisted living centers. Or, take them to look at some townhouses, apartments or homes near yours. Or, maybe you show them the airport and hand them a one-way ticket in the opposite direction you'll be travelling on your way home. Either way, you have options. Don't ever let yourself believe you don't.

Lastly, if none of the above got through, maybe this will: According to the US Dept of Human Services, only 6% of elderly parents willingly move out of their adult child's home after moving in. 94% of parents who live with their kids are there until they die or are forcefully moved out.