The building was given for free use, is it necessary to have a document in this case?

I have a sister, she has 2 children. She drinks a lot and is aggressive towards children. I talked to her about it, but she doesn't do anything to fix it. And my husband and I want to raise children. How should we proceed?

I plan to invite a friend to the wedding, he is from Turkmenistan, I need a visa.

My grandfather died, my mother is the only heir, but she cannot find the documents for the ownership of the apartment. What shall I do?