Why can't they play?

Set up playing assignments over exercises, scales, and small bits of music for your advanced kids. Do instruction virtually for your beginners and teach basic music techniques. Teach fingerings. Have them play from home, or finger-and-say notes if they're in person. Work on theory.

Use Flipgrid, Smartmusic, CHARMS, or even have them play off over Zoom in breakout rooms or via cell phone recordings for playing exams.

It's not ideal - but it's better than giving up and writing off the next two years of band.

It can be done, and it can be done successfully. Change your paradigm.