Your Guinea Pigs should each get one cup of veggies per pig per day. You will want to have a variety of vegetables but you will want to mainly feed romaine lettuce (NEVER iceburg), green bell pepper (1/8 pepper per pig) baby carrots (one per day is fine, not more however), and zucchini (1/2" per pig) are pretty much the 'main ones'. Don't feed fruits more than once a week, as they are high in sugars and can lead to diabetes.
For pellets they should get 1/8th cup per pig. This is two tablespoons.