As Jim alluded to, you need to be very explicit about gear. I've taken groups of 2-6 very inexperienced people on assorted trips, from strenuous dayhikes to backpacking trips. Here's things I usually make sure to include:
- Be very strict about no cotton clothing, and explain why. People may show up with cotton sweatshirts when they really need a fleece vest.
- Make sure their raincoats have a hood. Surpiring how many people overlook this.
- Require everybody to bring a change of socks.
- Require everybody to bring a warm bottom layer. People often bring jackets but forget to bring fleece pants or longjohns.
- Have a minimum amount of water that everybody must bring (usually 2-3 L depending on the duration). Just saying "two water bottles" isn't enough because people will show up with two tiny vending machine bottles.
- With food, people often underestimate their caloric needs when doing outdoor activities. For a day trip I usually tell people to bring a hardy lunch, enough for at least 4 big snacks during the day, and "backup food" that's enough such that they would be OK if they didn't make it back for dinner.
- Some form of lighting is a good idea.
- I usually encourage people not to bring certain items, that list depends on the trip and the group. Alcohol and smartphones usually go on the do-not-bring list.
Be prepared for somebody to forget something important. I usually bring an extra warmth layer, an extra warm hat, and some extra food (typically some compact energy bars). It's good to personally, visually confirm that people brought all the required gear. "Everybody show me your rain coat" not only ensures that everybody's coat is adequate, it also ensures that nobody accidentally left theirs behind.
As for group management, the most important thing is to check in with everybody often, and don't be afraid to turn back if people aren't up for your original plan. It's better to turn back before the summit than to end up in a bad situation with people who are exhausted and inexperienced. Sometimes people will be feeling tired, but they feel bad about holding back the group so they won't say anything. Keep an eye out for that.
Before leaving, make sure to ask each person if they have any medical conditions you should be aware of, if they typically carry any type of medication, and if so make sure they have it and that you know where it is. It's better to know people's basic medical info before it becomes necessary.
It's also important to keep an eye on your own well-being. It's easy to get distracted when taking care of 5 other people, but since you're the person responsible for the group, it's paramount that you're well fed, hydrated, etc. Don't forget to take care of yourself!