Without knowing for sure if percussion 2 can be played by one player, I would play it as safe as possible. There are 6 percussion parts. You have 4 percussionists. The judges won't penalize you for the parts you can't cover, but they might for a wrong note. Even if it's possible for one player to cover crash and triangle, even if there's 8 bars for them to switch, asking a kid to switch instruments on the fly is just one more thing that can go wrong. I would assign one kid to crash and another to triangle, leaving out the timpani and bells.

Musically speaking, at this level, the timpani probably double the tubas and the bells probably double the soprano winds. Unless your winds are really weak and your percussionists are strong enough to help them out, those parts aren't that important.

I don't approach the sight-reading contest (I'm sorry, literacy evaluation) as a chance to show off or have a great musical experience. It's a game to play. Use the strategy that gives you the best chance of scoring well in the game. Save the great musical experience for the concert stage.