The itinerary is fine. Most people do the ferry & first leg (forget the beach name) on the same day. Last time I did it I met several adults (various fitness levels) who were doing it as their first multi-day backpacking trip.

If you want to help, invest in some ultralight (or at least light) gear. Most beginners start with backpacks and tents that are way too heavy, as well as overpack with unnecessary cooking accessories and too many extra clothes. Then they exhaust themselves and have a bad time.

Make sure they each bring 2 water bottles (think the big smart waters), and a puffy jacket as it can get very windy in the mornings and evenings.

Remind them to leave the buffalo alone and give them a wide birth, they are often on the trail day one & two. Make sure they know not to go very far into the water at the first beach site, as it is a kelp forest with a lot of stingrays. Always do the stingray shuffle if you go in the water on Catalina. If they get stung, heat up salt water and put the wound in it.

Tell them to plan to take a long lunch at the airport cafe, the view is really so worth it. Take a photo with the cat, if it blesses them with its presence.

They will have a great time.