I recommend Lahaina Divers for beginning divers for at least Lanai. Although they take a lot of folks on their boats (up to 23 divers), the boats are super stable, very roomy, have a bathroom, and make for a very comfortable ride to and from the dive sites (less sea sickness). The entire operation is geared toward safety and catering to the occasional and/or beginning diver with shallower profiles and shorter dive times. They also have very nice rental equipment if you need it. It's a 45 minute drive from South Maui (Kihei, Wailea) to Lahaina, but it makes for a shorter, smoother crossing to Lanai.
For Molokini you have quite a few choices, especially if you don't mind driving early in the morning if you're staying in West Maui (Lahaina/Kaanapali/Napili). From the Kihei boat ramp, I'd recommend Ed Robinson's or B&B for beginners. From West Maui, you can stick with Lahaina Divers and enjoy the boat ride from Lahaina to Molokini. Gorgeous views!
Lahaina Divers actually serves sandwiches between dives on their charters, but you'll find that everyone else (at least on Maui) has some sort of snack (muffins, sweet rolls, pineapple, etc) before and between dives as well. Boats also carry fresh water and mask defog....it is definitely the Aloha State!!
Whomever you choose, make sure you speak with the dive operator and tell them you have junior divers, etc. They'll need to know that in order to put you in the right dive group with the right dive master.