I would suggest hiring a drum instructor. You're going to have a really hard time teaching these students the basics if you are barely learning the basics yourself. A tuba player doesn't really have much insight into a high school drumline I'm sorry to say. Try picking up Tom Aungsts new book, it has some good single and double beat exercises. But honestly you're not going to get these kids to hold a cadence if you can't even pick up the sticks with the correct technique. Give someone a few bucks an hour to come in once or twice a week...make sure you are there too, and take notes on what he is preaching, that way you can carry on the instruction without giving up a massive amount of pay.
Hope it was helpful. Best of luck. I hope it works out for you, you have a long road ahead. Where are you based out of, I know a lot of percussionists across the country through my time in WGI and DCI, maybe I could help you out....