I can't be happy for them

Me and my husband lost our baby a few month ago and we have just found out his brother and sister in law are pregnant. It's very painful and hurts because we have fell pregnant at the same time. My husband doesn't understand why I am being like this but I just can't help how I feel. His brother is in a toxic relationship and they are abusive towards each other and cheat and the kids they have already aren't even looked after properly. Me and my husband have our own home and financially stable and it's really hurt me having to pretend to be happy all over for yet another one of her pregnancies. All I want to do is be a mommy. I know it's a happy time for his family bit I have said to him I want nothing more to do with his sister and don't want to know anything to do any of it. Am I being to harsh? How can I stop feeling like this? Is this normal? I feel like I'm in the wrong for feeling like this and feel like I'm being spiteful and jealous. But on the other hand we lost our beautiful baby and I have every right to feel like this. I forgot to add she also smoked and drank all thru her last pregnancies and all baby's were born premature. She makes me feel sick to her stomach I feel like giving her a peice of my mind sometimes but I know that wouldn't help at all. Ladies please help me how can I stop feeling hurt and upset about this. I do want to be happy for them but I just can't😢😢😢😢