This isn't a real world job where you control the conversation, give 2 weeks notice and transition stuff. There's no good way to depart.
Just tell them you loved coaching them, you're leaving for a better opportunity, and wish them the best of luck in their future NFL or other careers. And tell them you'll be a reference for any one of them, in any capacity.
I probably wouldn't make them come to the football facility at 7 am, but that's the world we live in. You can't compete against social media. Guys like Thamel and others just have too many sources.