Ugh! What do I do?

SIL has just text me saying that they're paying for OH to go to Ireland for his birthday in March. I can't tell him any of this as it's a surprise so I'm stuck..

1) I will be 32 weeks pregnant.

2) I will have to pay for myself. It's not very expensive but we would have just spent a lot of money on the baby so I'm not sure we could justify the expense

3) it'll be 2 weeks before I go on maternity

4) families don't know we're expecting so I can't use this yet.

5) it is a lovely idea and I know he'd love it but I'm thinking logistically.

6) I don't want anyone to think I don't want to go as it's not about me, but I already went on holiday with his family last year and it was the worst week of my life and this will be spent seeing family and not sightseeing as I would want my first trip to Ireland to be like

What do I do? I've already said I can't book time off so they've said it's a friday-Sunday trip.