I feel like I shouldn't congratulate my pregnant sister.
Why wouldn't you congratulate your own sister?
Because I'm so envious of her, man...
This is big news for her, man!  You need to set aside your personal grievances and celebrate a special event in your siblings life!
Maybe I would, but she was hiding the pregnancy from everyone and I think she deprived me of any delicious meal ever since she knew she was pregnant.
Those all sound very petty, and you should care more about family. How would you feel if you had extremely huge news and your own family didn't congratulate you or seem to care?