Ah, ok. So the real breakdown here is due to the parents figuring K will not do much more than run down the courthouse, and that C's baby takes precedence over whatever K is doing.
So it doesn't really change my answer all that much. Unless K is planning a destination wedding, there's still a good chance that C will be able to attend. And there's no reason at all that the parents can't attend. Even if C is in labor at the exact time of the wedding, the parents do not need to be at the hospital holding her hand. If she hasn't had the baby yet by then, everyone can be at the wedding. If she has had the baby, C can determine if she is up to attending the wedding but the parents really have no excuse not to be there unless C is going to be happy with the parents hanging around with the new baby 24/7 which is pretty doubtful.
So really, in my opinion, the only reason for K to change the date is if she wants to make absolutely sure C will be able to be there. In that case, it's between C & K to discuss and work out.