I need advice

Hi moms to be. I need help. I'm going nuts here. Input would be greatly appreciated. 
My husband and I are expecting our first child in september. I'm a high risk pregnancy. My sister in law, who happens to be almost 40 yrs old, has been giving my husband and I grief since she found out we were expecting. She has been having problems conceiving herself and has undergone 2 rounds of IVF unsuccessfully. Anytime anyone gets pregnant she becomes irrational and causes a lot of problems. She's getting married 2 days after my due date and started crying when we told her about the pregnancy. She said the baby would steal the spotlight from her wedding and that it wasn't fair that she wasn't the one to have the first baby.
She asked us both to be in her wedding party and we initially agreed - even though we felt disrespected that she also insisted on disregarding our feelings and including my husband's ex-gf and her son in thewedding  party.  However, when we found out we are due 2 days before the wedding I said I would not be able to be a bridesmaid and my husband, who decided on his own and without my influence, said he wanted to accompany me on that day and felt it would be more appropriate to be near me in case I need something, instead of away from me during wedding party pics etc. so now  she's making our lives miserable. She disowned my husband, uninvited us to the wedding, and is telling all of their family and friends that I'm jealous of the ex-gf and won't allow him to be in the wedding bc of it. The problem is that no one in the family is seeing our side, they are all angry with him and say he's wrong for choosing his wife over his sister. In our eyes he's not choosing me over her, he's trying to be a good husband and father. Are we being selfish? Is it ok for him to say we would be at the wedding but not in the wedding party? Or are they in the right?? I'm lost. I'm losing sleep and stressing my baby because of this high school drama. Input please!