I recently posted a sort of similar question to this about in laws, it was about my in laws making me want to end my relationship. My partners parents are lovely, its his brothers and their partners who treat me like something they have stepped in, they love each other - God knows what I ever did wrong, perhaps they don't like the fact I was divorced, who knows and that's the very point. It is a really dangerous thing to speculate on why they are funny to you and fine to their other sibling, you may find yourself going mad trying to understand it, so don't! If your partner does not care about them disowning him, you should not really (even though I know I would). Do not let this ruin your wedding though, sit down and talk to your partner about possibly having a meeting and getting whatever appears to be on their chests out in the open. I know exactly where your coming from, because I actually put off possibly marrying my partner because I do not want the hassle of my potential bitcy sister in laws! At the end of the day though, your wedding day is a day for you and your partner, so talk to him, see exactly what he wants, discuss ways of resolving this, but just remember if they have a problem with you, its usually because they have got a problem! I thinks that makes sense. Good Luck though, your not alone with this dilema,x