Guinea pigs that have not had veg in their lives before often struggle to accept them at first and can be very hit and miss once they do. Be patient and persevere!
Try fresh green stuff first. Most piggies find a handful of fresh cut grass (make sure that it is free of any poisonous dog pee), fresh parsley or cilantro/coriander, lettuce or a bit of spinach quite irresistible. Spinach is very high in calcium, so it should not be part of a daily diet, but it is a good "lure" veg, so don't hesitate to use it at first until you can establish a regular diet if Toothless loves it.
Generally, the best thing to get them to eat is the "I want what you have" reflex when living with or next door to a mate and can watch the other piggy eat. Until then, you just have to sit it out and try your best!
Fresh mixed veg should make about a cupful/handful per piggy per day in as many servings as you like (that is about 10-15% of the daily food intake - hay should make up to 80%). Please try to include at least one high vitamin C veg like a slice of sweet pepper of any colour, a sprig of parsley or cilantro, or a floret of broccoli every day and vary between them once you have established a regular diet. Otherwise, you will get furthest with giving everything in moderation and varying the diet; you will need to find your own balance between what your piggies eat, your purse can afford and what is available to you.
PS: Unlike some advice you may come across, you can feed cabbages, even daily (I have done so for years now without any problems); they are actually not a bad source of vitamin C. But introduce them slowly and always as part of a veg mix. Take them off the menu if you have a piggy with an iffy digestion and a tendency for bloating (but with those piggies you have to go through all veg singly to find the ones they can't cope with).
Here are a couple of links about piggy diet:
http://www.theguineapigforum.co.uk/showthread.php?t=42
http://www.guinealynx.info/diet.html
Please weigh your piggies weekly. It is an important tool to spot health problems early on when they are still treatable. Food intake can be deceptive; scales don't lie!
http://www.guinealynx.info/diet.html