First - gorgeous piggies 
You need to do a balancing act with them .
Their pellets will be a good source of Vit C and fibre
They need hay (about their own bodysize but really , unlimited)
Fresh water
Then you look at the types of veg
Not too much fruit - they get fat , can risk diabetes , can make them loose
Not too much dark green - can make them prone to bladder and kidney stones
Not too much calcium rich (brocilli , herbs) risk of bladder stones
Not too much root veg (high in sugars)
No: potatoes, iceberg, mushrooms, stoned fruits, onions
They are complex little animals , they cannot make their own Vit C , they cannot be sick, they cannot go more than 7 hours without food or they risk liver failure .
Give them pellets not muesli-type dry food but keep them on whatever they were eating for now -if you do change foods , do it gradually mixing in some new pellets to the original ones .
Honestly - a flipping Gremlin is easier 
I;ll be back anon , enjoy your piggies.