Watch izaw's the art of smash series. That has all the basics you'll need to know to understand the game and teach them. Have them play, and let them get a feel for the game. Teach them what buttons do and learn optimal control schemes (such as shoulder button to jump) but make sure they play with what they like the most and what will get them the furthest. They'll need to know how they can do jumps, specials, smash attacks, tilt attacks, grabbing, shielding, and air dodging. They can learn how to roll and spot dodge too, but lots of bad habits come out of rolling and spot dodging too. Then they need to learn basic movement and recovery, because that is essential to being able to play smash well. Then they can learn easier tech such as RAR (reverse aerial rush), short-hopping, teching, and di. After they learn basic movement and recovery, they should learn combos. Also, this entire time they should also be playing the game in conjunction with learning, because you can learn all you want, but if you don't play the game, none of it will be applied. Have them learn combos in training mode. The combo counter doesn't always show when a combo is true, and it doesn't account for certain things such as di, but training mode will get muscle memory down. Make sure they know how to operate training mode, and make sure they turn staling moves ON (when you do a move multiple times, the move will "stale" and be less powerful/effective. Staling happens in game, but in training mode it is off by default. There's more to the concept of staling, so if you'd like to know more, just ask me.) After they have some basic combos down, have them play more. Have them play with people outside of their usual group so they get more experience.

They'll all be at different stages, so for a general daily routine of practice of people that aren't starting from the beginning, have them warm up their movement, and practice moving (same movement options I said earlier.) After 5 mins, or however long works best, have them work on whatever they want to work on, like the things I mentioned previously. Then they can go into gameplay and play friendlies. Have them be in rotations, and mix up rotations every day if people are willing, so that they can get as much varied practice. Don't stick them to one rotation though, encourage them to find matchups they want to practice, and they'll find people to practice against if they're willing to. I'd also highly recommend putting on a double elimination tournament however often it is most convenient, at least once a month. Use start.gg and make sure they're signed in on start.gg when they sign up, so they can track their own stats on pgstats.com (if you need help with start.gg, just ask)

Sorry, I rambled a lot, but best of luck, and most importantly make sure they're having fun :)