They live in the dining room in a cardboard box. We have been letting them out for increasingly long periods of time. Once they are completely sure of where their home is, we will cut a hole into the cardboard so they can come and go as they please.
There are three main reasons for keeping them in the house, other than it lets us get familiar with an animal that's new to us.
1) The kids LOVE them and play with them constantly.
2) They eat all the scraps of food that the kids drop at the table, so help me "sweep".
3) Their scent will apparently deter mice or rats from entering the house. If this is true, we will definitely get a family of them living in the barn.
Leo named them - the female is Essy and the male Ping. Ping is about as laid-back as any guinea pig could possibly be. We are a little worried that he might not be effective as a breeding male, as he seems to think of nothing but hanging out and letting the kids hand feed and pet him. Essy, on the other hand, is extremely active and adventurous. She doesn't let the kids boss her around at all and it has become the new family game (it needs every one of us) to catch her when it's time to go back in the box.
So far, they are a fun addition to the family. We'll see how it goes.