I asked the same question some time back and several people thought that it would not be a problem. We have APs and plan to go for a few hours before the party, too.
I especially don't think your costumes would be a problem. Disney might challenge an adult wearing a Disney costume that looked very realistic, but I'd be surprised if anyone challenged you on a party night (even before the party). The way you have described your costumes, I have seen people wearing odder clothing on a normal day.