Someone was offended by something I wrote recently. I apologised because I felt terrible. It actually turned into an inspiration for a new story (as you said). Then someone commented on the story and sent me a quote by Stephen Fry:

“It’s now very common to hear people say, ‘I’m rather offended by that.’ As if that gives them certain rights. It’s actually nothing more… than a whine. ‘I find that offensive.’ It has no meaning; it has no purpose; it has no reason to be respected as a phrase. ‘I am offended by that.’ Well, so fucking what.”

I’ve read the story that had offended your family member and as you said, everyone is entitled to have their own opinion. I think you’re just being honest and that’s a courageous thing not everyone can do so keep writing! :)