Extremely Bitter Sister in law!!

Hey ladies, so I just wanted some advise on how to deal with my sister in law. So I'll try and keep it short...My sister In law is mid 30's and has always gone from man to man cheating on the current on with the next, but always trying to make out she's the hard done by one all the time!  She's openly said she wants to have a baby and settle down but doesn't think anyone is good enough for her, and on top of that she also struggled to conceive.  So late year I got pregnant and she had the mother of all meltdowns and her mum (my mother inlaw) then joined in and went mental at me.....this lend to me having a termination, Becuase I didn't know how to cope with those two, and the timing wasn't great for me and my DH
Anyway fast forward to now and we're pregnant again (6wks) and completely over the moon but I know they won't take it well when we tell them (at 12 weeks) we all live very close together so I can't just avoid them, but don't know how to deal with her!? had anyone had to deal with this? what do I do? xx