Hi, your piggies are always going to be skittish. Only about 10 percent or so of pigs ever get what you would call "tame". They will always run from you but the more you handle them, the faster they will eventually let you pick them up. There are lots of tricks to getting them to be easier to catch and if you keep them in a busy part of the house with lots of human interaction it will help. My friendliest pig was a mascot for a pet supply store and he's SOME PIG. Afraid of almost nothing he chases my puppy around the house!
Baby guinea pigs will nibble on you quite a bit. Much like a puppy, they discover their world with their mouths. They do outgrow it, and I've never heard of them ever biting ..just nibbles. Especially if your fingers taste like veggies!! Just make sure to have something yummy to nibble on when your holding them instead of your fingers. Guinea pigs are full grown at one year of age or so and live to be 7-9 years old if properly cared for.
I'm assuming that you've set your furries up in a nice large CC cage, in a nice busy part of the house, and given them LOTS of places to hide and feel safe. I find that the more they are exposed to you, the more they get handled, get veggie treats (I never pass a piggie without offering a little veg if possible) and learn to feel safe around humans...oh and don't forget that sometimes they start nibbling on you when they have to pee..I have 2 pigs who don't nibble until the ole' bladder gets full.
Here's a couple links about taming piggies that might help:
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Guinea Lynx :: Behavior
Also, it's very important that you learn about your cavies as much as possible. The link below will take you to the best advice on the web, especially for a newbie. Explore this care guide by clicking on the blue lettered sections. Once you have really learned everything in the "care guide", go ahead and explore the Guinea Lynx site and take a peek at their forum. GL is considered THE place to go for learning about health of guinea pigs. Their forum is for advanced care-givers so when you get more complicated questions they are a great source. Many of the members are Veterinary Professionals.
Guinea Lynx :: Guinea Pig Care Guide