Not sure whether I'm being incredibly petty or right for feeling this way.
I am currently 37 weeks pregnant with my first baby.
6 years ago my mother married a man who is a bit of a prick, not to the level of being abusive to her (in which case I'd not even post and be LC/NC)
Mum is a CSA survivor so often has patchy taste in men, as she has experienced the worst you can and so anyone who even shows a shred of decency is great in her eyes, am adding this for context as she really isn't to blame in this situation imo.
A few years ago we went on a family holiday together, me, my DH, my brother (who has ASD), mum, her husband and her husbands children (3 adult children)
DH suffers from anxiety and depression, it's well managed and has been for decades, but he does sometimes struggle in larger groups, one day during the trip it was getting a bit much for him and he did look withdrawn, he wasn't rude but not his usual self and looked a bit down.
I overheard my mothers husband saying to 2 of his kids 'the dopey fucker looks miserable as shit again, maybe he can fuck off for the day' and it was clearly in relation to DH.
I took him to one side and told him he is to never speak about my husband like that again, my mum overheard and it kicked off. Her husband admitted making the comment, he and mum then had a massive argument about it, where he made nasty comments about my brothers SEN, that night mum came into our hotel room to sleep as she couldn't stand being around him.
The next day however it was all patched up from her end, DH, my brother and I then didn't spend the rest of the trip with them as we were still pissed off.
In the years since this incident I have kept a bit of a distance from her husband, my DH however has tried to build a bridge as he doesn't want to be the cause of any family drama and has done a damn good job of making it look like all has been forgiven.
As mum actually thinks it's all water under the bridge.
Which is why she is thinking it will be all fine to have her husband known as grandad to our DC. I however really feel uncomfortable about this, I don't like the man, but to raise this would rehash the entire holiday incident again, she genuinely thinks it's all forgiven but I don't think I ever will. The comments he made about DH - knowing he has depression and the comments about my brother crossed a line for me.
But I don't know whether I am being petty about this, I'm prone to holding grudges so don't trust my own gut, as I still haven't forgiven the neighbour who ran our bin over 8 years ago 
Would this be a hill you'd chose to die on so to speak?