Are these pigs that the person needs to rehome because she can't keep them, or did she breed them?
As far as keeping them longer, there is no need to. Baby guinea pigs don't need their mother's milk like kittens or puppies. They are fine within a day or two on water, hay, pellets, and veggies just like Mom would be. Please make sure that the person you're getting these guinea pigs from understands that a baby boar can be sexually mature at 3 weeks old, and if his mother or sisters goes into heat, he will mount them and get them pregnant. This would almost certainly kill the baby sows, and getting pregnant again so close together could very well injure or kill the mother pig.