I take for granted you will pick a song that all can relate to and that everyone will be playing from the same sheet music. Never before bassists only need to keep the beat and lets hope they can change roots dead on when the changes happen. Beyond that I would not go any deeper.
Notes in the first position (first 5 frets). With C as the home note.
- D is over two frets from the C.
- The B is one fret toward the nut from the C.
- E is over the B.
- F is up a string same fret as the C.
- G is down a string same fret as the C.
- A is under the D.
- That takes care of the roots they will need.
Rhythm is next and perhaps the hardest to teach. I'd let them have fake chord sheet music which gives the lyric word with the chord name over the lyrics. Follow the song's lyrics and this should help with the rhythm beat. Have them sing, or recite the lyrics, as they play. This should help with the rhythm.
First day someone will have to teach them how to hold their bass, how to tune it, how to get sound from it and how to mute the growl.
May take all day that first day.
I took claw hammer banjo lessons with about 20 other people at The George C. Campbell Folk School 20+ years ago. We were able to play, as a band, our first song in 5 days.
Mornings were "show and do" and afternoons we split into one on one sessions with an instructor for about 15 minutes each. There was jamming in the cabin after dinner. Some of the more experienced students helped the newbeys with jamming and this turned out to be a great leaning experience..
Sounds like fun. Good luck.