There are no good guinea pig books out there. 99% of the info is junk and should be ignored. You can start handling the pups now but carefully. They can be nervous and jumpy though so don't lift them out of the cage the first few times you scoop them up and if you transport them to another room put them in a box or something. I usually have them out for floortime in a playpen with veggies and hay before 3 days old.
Here's mom(brown), her cagemate who was around 3-4months old, and her three 2 day old pups out running around with fresh alfalfa and lettuce to eat.
http://img.photobucket.com/albums/v2.../P10100482.jpg Granted they can't "run" very well at that age but they toddle along. Handling them young is great because they deal with people much better in the long term. They only get jumpier the older they get with no handling.
In a petstore cage the mother may decide she doesn't have enough space and pick on the other pig. Plus they are gonna really fill that cage up when they start bouncing around. You better start getting the materials for a c&c now while they aren't quite as active. It only lasts a couple days before they are bouncing off the walls.