R.:
If you haven't sent out the invites for Rob's party - yep - you can reschedule - you've got a LOT on your plate right now - your family, your wedding and all the other stuff....
I would go to the baby shower and plan Rob's party another day - THAT will be the surprise for him (we did my husband's 40th as a surprise party one month early - planned my son's baptism around it too so we had an excuse for family to be in town!!)
I realize you guys have had a tough year so far - he's still recovering from his hospital scare (that's a poor word to use but I can't think of anything else right now)...since it's not a "big" year - wait and do his surprise party for a BIG year - 40....or do something like a 49 and a half...something like that....but really - with all the financial stress you guys have been under - don't put more financial stress on you to plan a surprise birthday party and a wedding in a 45 day time frame......
GOOD LUCK!!!!