J.H.
I don't think it has anything to do with genetics. Every family has a culture, and when you merge two families you have cultural differences that are often hard to see. I have had no problems with any of my in laws. But, one of my brother's girlfriends had it in for M.. Some people are insecure and compete for love and attention. I don't understand it either...
As for your boyfriend and your daughter - give it time. I use to think you can easily love a child that is not your own but it's not that simple. Don't test him J. give them time for their relationship to develop.
Best wishes to you!