[X] The Experienced Umbreon - Skilled enough to know Assurance and Hyper Beam while capable of acting as a trainer, he would be a valuable Pokemon to catch but also the hardest to catch. He would know the most about what's going on.
[X] Send Chansey to assist the other trainers - Losing the healing ability of Life Dew will be difficult but manageable. Then again it would mean that other trainers can get their Pokemon in the field once more.
[X] Send Dragonair to assist the other trainers - Avoiding super effective ice moves from Glaceon, the loss of your sweeper will cause this fight to be harder. But he may win the other battles quickly.
[X] Send Magneton to assist the other trainers - Losing the special attack capability could be problematic, but he's poorly suited for defeating the Umbreons who are the most dangerous.