We do this every year, but we do it at the end of summer band. Schedule is something like:

8:00 students report to the field. Parents to the band hall for the beginning of season parent meeting. My staff are outside with the kids warming them up, I'm inside with the parents.

8:30 parents go outside. The kids are in their warmup block. Parents stand next to their kids and we go through some marching basics. Standby/set position, instrument carriage. Every step of the way I have the kids demonstrate, then parents try, and then kids get to correct their parents. We do 1 step forward, 4 steps forward, maybe we get to backward. Kids demonstrate backward march, slides, box drill. I jokingly tell the parents now it's their turn for box drill, but I don't really expect them to.

9:00 parents move to the bleachers. Kids move to a standstill formation, we play the fight song and a couple of stand tunes, then we play however much of the show we know (maybe the opener if we're lucky).

9:15 done - boosters have a table set up, parents can find me and ask questions, but that's really it.

I've never tried it at the end of the season, but I can see how that would be fun. I've never seen the parents actually try to march anything more than basic fundamentals.