It's one thing to post pics of yourself, but I think it is a really bad idea to involve family members. Especially if it's your children. But as for other family members like your mon, dad, sisiter, brother, I would ask them first.
Always have someone's permission before posting their picture - preferable a writen ad signed agreement for your protection and theirs. Understand that minors cannot make this decision, thus an a signed agreement with one is invalid.