I moved into the 'granny flat' here 3 years ago, it was great at the beginning but then SIL went really strange for about a year, he was getting upset because it was me not his Mother(dead for 17 years) living here.
The air got cleared when I lost it with DD and she lost it with him.
Now I would not want to live anywhere else, but it was walking on eggshells for a while.
The main thing I have found is not to, 1, interfere in any way, 2, do not expect to be invited to things with their friends, and have a joint diary with regard to babysitting etc.
DD asks me about everything, we are very close but we have our own places and respect each others privacy.