Will they be housed inside or outside?

The skin problem could be from mites, ringworm, or lice (humans can't catch the type of lice that they have so don't be worried, Taffy has had if before, nothing a vet can't treat) they can catch mites and other bugs outside, so since they have been housed out there its probably some sort of bug.

Make sure to sex them when you get them. Double check they are all females! That is really important so you don't end up with baby piggies! THIS page has very good well written steps on sexing a guinea pig.

Have your piggies on a pellet diet, they don't need seeds! Some brands have the 'colorful' food. They don't need that either! Food coloring isn't any good for them, and I've seen that most piggies just spit the colored pieces out! They will need 1-2 salads of fresh fruits/veggies a day. Try spinach, lettuce (just not iceburg), carrots, apples (not the core or seeds, seeds are toxic), red, green, or yellow pepper, strawberries, oranges (good for vitamin C), and pretty much whatever veggie you woule eat. But don't give them grapes or mushrooms! I'll try to find the whole toxic food list, but those are two pretty common foods that are toxic to a guinea pig, one mushroom can kill them within 48 hours!

Make sure that they always have a fresh supply of timothy hay, if they are under a year or under weight put them on alfalfa. Alfalfa has too much calcium for grown piggies unless they are pregnant or underweight.

NEVER put them on cedar bedding or non kiln dried pine! You might already know that because I beleive it is the same with rabbits. Kaytee Pine brand is kiln dried and works very well if you can find any.

Feel free to PM me if you have any questions. I'll post some links for some good guinea pig sites:

cavyspirit.com- good general care tips
cavycages.com- how to make your own cage, very helpful and the cages are easy and cheap to make, too!
http://www.guinealynx.info/forums/index.php- great forum, especially their emergency forum, they have helped me out with Taffy when I really needed it!

I'll try to think of more of my favorite sites for you later, but if you go to google and search Cavy Care lots will come up.

Good luck! I have to see pictures of your piggies!