Adopting Adding more guinea pigs to our pair

We have a pair of 6 month old females, which we got at 5 weeks old, that are doing great. We got them from a locally-owned pet store, which was our best option at the time (we live in a smaller city where there are no rescues and only occasional listings online, and we were being impatient) and they were not in the best of health (lice, missing patches of fun, scrawny). However, they are thriving now and my two daughters, 8 and 10, are great with them. I maintain the cage, they help with feeding and play/spend a lot of time with them. We feed them a very high quality diet (Oxbow products and lots of fresh veggies, no store bought treats/crap).

We have a 2x5 C&C cage. We are planning to add a 2x2 "L" section, where we will place their hidey and a fleece forest so that they have the run of the 2x5 area.

One thing we are considering is adding another another pair of females to our pair. I know that cavies tend to live in groups in the wild, and I am wondering if it would make them happier being in a larger group? They are by themselves from 8-4 Mon-Fri. They have each other but I am worried about them being bored. They are really not into toys, so maybe other pigs would liven things up a bit? I know there can be issues with personalities when you add piggies. We have a Midwest cage that we can use for initial quarantine, and we can expand and separate the C&C while the pigs are getting used to one another.

There has been a lone pig up for adoption in our area for a few months now. She was initially a rescue and now is 3 years old. I would bring her to the vet to make sure she is female. The plan would be to keep looking for an older pig as a partner for her if three's a crowd. Or, would it be better to wait for a pair of bonded females to adopt? They are pretty rare around here, most pigs come from the pet stores and tend to be male in our area. I think this particular pig has been alone for most of her life.

Is this a good idea or am I just rocking the boat? Our two girls get along super well, and it does not seem like one is dominant at the moment. The only time they squabble is when they don't have space, like when they are in a small cage because we are traveling or cleaning their C&C. But even then, it tends to be just a few seconds until they get comfortable. They came with us for xmas vacation, 12 hour car ride there and back and they did great. They are pretty mild mannered. We have no other pets in the house. Extra cost is not an issue. My goal is to ensure that our two pigs have a happy life, and to accommodate another pet that could benefit from a better standard of living.

Thanks!