Honestly, I don't know! :-)
If those same people are all travelling for the wedding as well, then it might be a lot for them to do, you know? But if this is a different group of people who won't being doing the wedding related travelling, then they might not mind sneaking away for a couple days?
IMO, I wouldn't want to ask too many people to travel 4 hours for a party. Did your parents say who they were wanting to have there?
This is a tricky one! Good luck!