I have had house rabbits for about twenty years now. I have also rescued rabbits, too. The best place to get information on what to feed rabbits is at
House Rabbit Society. Domestic rabbits do best on a diet primarily of hay. Timothy is best but any grass hay is good. Pellets should make up only a very small portion of their diet. My current rabbit is only about 4 pounds and he gets 2 tablespoons of plain Oxbow Timothy pellets twice per day (don't feed those pellet mixes with all the junk in them). He is free-fed hay and also gets fresh vegetables twice per day. His favorites are parsley and dandelion greens, cilantro, dried carrots. The vegetables help to keep them hydrated, too. The website I mentioned has lists of safe fruits and vegetables for rabbits--but not too much fruit. Plenty of fresh water is a must. While I have a dripper bottle, he prefers drinking out of a bowl so I have either available at all times. They also need things to chew on; the little Timothy cubes at the pet store (Kaytee is one brand) are a good thing to feed. They need room to move and exercise daily.
Rabbits can be fragile but if you feed them properly and give them exercise, they can live 8-12 years.