Melle

Ok, i'm not happy with my future sis-inlaw, about 2 days ago my H2B got a call from his younger brother to say that his wife is pregnant, i don't really care for kids (one of the reasons why i'm not having any children younger than 18 at my wedding) and she didn't congratulate me when i got engaged so i didn't say anything to her when she said she was pregnant but what has really made me made is she has done this kinda crap before to get out of seeing my H2B's family, her baby will be due around the time of my wedding, i think she planned to get pregnant now as a reason not to come to my wedding and i know she'll try to stop her husband from coming too (they live in Melbourne, we are in Adelaide).
She doesn't get along with my H2B's twin sister and his mum. When my H2B's mum got married in Feb this year, she didn't come, she claimed she was pregnant back then too then like 1 week later she said she had a miscarriage, i don't believe she was even pregnant in the first place coz when my fiance and i visited them in Melbourne in Xmas last year, she told me she was going to make up some excuse not to go to her mum in laws wedding coz she didn't get along with her.
fsil (Future sister-inlaw) also has bipolar disorder and she doesn't take medication for it, if she stops my H2B's brother from coming to our wedding, I'll never have anything to do with her again, she's done other manipulative things in the past.

What would you do in my situation?