This isn't the 1800s, why does OP not use a mobile phone to communicate directly with the sister getting married? What does OP plan to do once the baby is born? Continue the transient lifestyle? Dysfunctional all around
The boyfriend sounds like a child who's never been told no by his parents. Also sounds financially irresponsible. With that much difference in fiscal priorities, I don't even think I'd have let him move in, or continued a relationship.