I'm not going to support my mom's pregnancy
Why aren't you going to support your mom's pregnancy?
This is a world with a lot of problems and kids should not be brought into all these troubles.
You need to support the decisions of your family members. It is always a happy occasion when a baby is born. That will be your sibling and if you do not support your mother's pregnancy then you may be limited in how much you are allowed to see your sibling.
I don't know how things will turn out.
You don't so you should support your mother. Things might work out well and you will want to have been there.