I really think that flying biplanes for such an Open House field day show would be a big hit, and I think I will build a Spad (although I'd prefer an SE-5), for the fun of flying it, but the amount of work (two wings!) getting it in the air would keep me from entering a combat match. But as per my prior comment, the pilots should follow a script, and there should be an announcer, telling the spectators that it's a duel with models and streamers, over what insult or misbehavior or whatever that a nasty "Hun" has committed, to be made right by a Hat in the Ring American volunteer, etc.
The pilots only need appropriate goggles (which can be worn Desert Fox style, on a hat), neck scarves, and distinctively colored shirts, not really flying suits or anything to simulate those.