We have my MIL living with us now (since last September). What makes it work for us is that she is in good health, can help out watching the kids when necessary, and she has a whole floor of the house as an apartment (we live in a 4 level split where we remodeled the basement level to include a kitchen, living room, bedroom and bathroom). She loves it. So far so good.

"Old people lose their hearing and turn the tv up way too loud."

Wireless headphones for this. Never hear the TV in another room.

We tried it and could not make it work, but our house is very small. It sounds idea from PP but often depending on what is going on, its not that easy. Idea is a 1st floor suite with a bathroom, bedroom and living room. If you have to hire someone, they need a place to be with your loved one.

In addition to the full bath with the bedroom on the first floor, get a tub with a bench built in, or a shower stall where you don't have to step over a "lip."

Definitely sound-proofing. Old people lose their hearing and turn the tv up way too loud. Also, a mini fridge in his area if the kitchen is on a different floor so he can wake up in the middle of the night and have a midnight snack easily.

Make sure there's a system where you'll know if he's left a door unlocked, whether he's in or out of the house.

One thing to keep in mind is that older people tend to wake early, not be able to sleep through the night, and tend to want to eat dinner early. Like, super early. Like 5:30. My mother pushed my grandfather to 7:30 when my father got home from work but I think that was too late for him. I don't know why she didn't just give him his salad when he got hungry to tide him over (she refused to serve dinner until her husband (my father) was home from work).

Also, keep in mind that in our society we throw away our old people, but they're a wealth of practical advice - fights with friends, squabbles with neighbors, work problems - and love being asked for help. Sure they can't use an iPhone, but they will light up if you get your kids to ask about Grandpa's first job, being in the army, when he first fell in love, homework help, etc.

Even though my grandpa lived with us, I don't think he felt useful. I wish we'd EACH made a point of spending a little time with him each day, whether it was going out to help him wipe down his car (one of his favorite outdoor activities), come with us to run an errand, talk about classes we were taking, ask him for help studying, whatever. We could have done better.

Sound proofing. OUr walls are thin, and sometimes we need to have privacy. For 'couple time', but mostly just to have conversations w/o eavesdroppers.

First floor bedroom and en suite full bath are essential.

We aren't quite there yet, but think the odds are good that we will consider having my FIL live with us in the next 5-10 years. So still a ways off, but we are in the planning stages of a house renovation (that we initiated when this wasn't even on our radar) and so I'd like to at least think this angle through.

So if you have had a parent or IL live with you, how did it go? What made it more difficult or easier? Things you would do differently or change?