[GeeTwo]

Falconmaster covered a lot of the key points. A few others that come to mind:

The #1 problem right now (based on what you wrote) is trust. Team members should not feel the need to vent about other team members to third party team members very often. When they do, they need to know it's going to be in confidence. If you don't lick that problem, you'll never fix the others, either.

While your change may come from the "grass roots" (and that's probably the best place for this to start, with an off-site meeting of current juniors and sophomores and a few others), you have to have top cover (from your head coach/lead mentor/school administration) for your leadership structure to stick. Creating a team manual would likely be a useful tool for this process (though it is neither essential nor sufficient).