I don't know how to be happy for her

Amy • Mom to 4 beautiful girls. 3/3/10, 4/27/14, 4/8/17, 3/7/19.
My sister in law think she's pregnant and I just don't know how to be happy for her. Her marriage is a mess, the two year old they already have is a terror, they don't have a place of their own, they spend their money like children, etc. they shouldn't even be trying for baby. The whole family always seems to have to come together to help them cause they can never seem to work out their own issues and always drag everyone into it. They HAVE to go on dates at least like 3 times a week or the marriage is in "shambles" they leave their kid with everyone all the time, even Walmart trips like every single time....
I'm 3 weeks out from having my last baby, sounds selfish and petty but I just want my extended family to focus on me and my family for once and tell me I'm a good mom and not worry about dumb drama with immature people because "we need to be so happy and supportive of the immature couple..." I'm so over it. 😪