Granny flat

I don't suppose it would be at all applicable here, but I have heard of cases where families have done this, only to run into problems later because the person in the annex needs a care home. If there is not enough income/assets to pay the full fees and the council has to foot most of the bill, they are apt to take a very dim view of that person's money having been used to make a substantial and valuable addition to a son or daughter' home.
Whether it's been done with that intention or not, it may be seen as 'deprivation of assets' and councils have been known to demand that the money be paid back.

Thank you all again.
I guess I was hoping to hear of some people who had done it successfully.But I will Definatly think on all replies.

I feel this is a recipe for disaster. If in doubt do nought.If you were sure you wouldn't be asking I think that in its self answers your questions x

I think the vital point is "unpredictable DiL".
Even if you heard dozens of stories from people who had made a success of it with their own unpredictable DiLs, that would be no indication of how you might get on.

Just to put the worst case scenario, as happened to my MiL, she sold her bungalow and paid for a granny flat to be built attached to her daughter's house. Unfortunately, her daughter and son-in-law's marriage broke up and the house had to be sold and she was homeless. Her brother, who was a widower, kindly let her move in with him. As I said, this is the worst case scenario but it does take a lot of thought.

Would not do it, I love my son and gc to bits would not want to leave that near to them we both live our own space. Also what happens if they need to move or give up the house for any reason!. Sorry to sound doom and gloom

Thank you all.
I know you are all right,my friends are saying the same thing.