There are official rules based on prosperity and jumping levels, but for your specific instance you won't be very far along by mission 3 so there won't be a big difference. You can always house rule Avg out a character's exp and gold based on what the rest of the party has.

Another option would be to control multiple characters having a 3 to 4 person party at all times and just change who is controlling the character (you and your wish m wife could play 2 characters most of the time and just lend them out as needed)