Over forty years ago we did this with my in-laws, I was reluctant from the start, but everyone else was so enthusiastic, I felt at the time I would be a real spoilsport if I refused.
We bought a big house between us, to be honest, we put in less money, and had more house, but I was never really comfortable with the arrangement. My mother in law couldn’t actually help interfering, it was undoubtedly with the best of intentions, but it used to drive me mad. Of course there were babysitting advantages, but I think on balance, I’d have preferred to have got a babysitter.
We stuck it out for about ten years, no real damage was done, but I way so glad to get out.
We are now multi generational living again, our daughter came home over a year ago with three children. I can’t say it’s without tension, but generally it works quite well. I can’t stand the mess, but accept that for the moment it’s their home, and they need to be comfortable and happy, but I’m looking forward to the day my daughter announces she’s saved enough for a deposit!
If you are going to go ahead, be prepared for compromise and practice biting your tongue.