To the OP, get yourself trained in first aid, and carry a decent first aid kit. You need to be able to at least have a crack at dealing with injuries, and as you have set yourself up as the ride leader, when the pooh hits the fan, the group will most likely turn to you to sort it. I would say that a decent first aid kit and the skills to use it are at least as useful as an inner-tube and tyre levers. If someone gets a puncture it's a ball ache, if someone gets hurt it suddenly becomes much more serious than a minor inconvenience.
Good luck, it's a bloody minefield being a leader.