You cannot add any other piggies into the same cage as a pair of boars. This will cause fights, broken bonds and single piggies. Boars need to be kept in pairs only.
Even if your boys were neutered and the pregnancy risk was not there, you still cannot keep two boars with a sow(s) as the boys would fight. It is one neutered boar to any number of sows only.
If you want more piggies, you will need to have an entirely separate pairs of boars in a separate cage, and they must never have physical contact (ie separate runs, separate free roaming floor times etc)
I would not be tempted to even get a separate pair of sows if they are to live in the same room as your boars, particularly given one of your boys is a teenager and one is still yet to enter his teens.
Adding sows into the same room (but separate cage) will cause a strong reaction in your boys and potentially still cause them to fight with each other.
If you were to have a separate pair of sows and they must be in the same room, then they would need to be in stacked cages with the sows at the bottom, so the risk of the boys smelling them is reduced and you must never handle the sows before handling the boars (always boars first so you dont risk transferring smells). This isn’t a guarantee though, it would simply be safer for the sake of your boys relationship to have a separate boar pair.
The guide below explains further
Adding More Guinea Pigs Or Merging Pairs – What Works And What Not?
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
A Comprehensive Guide to Guinea Pig Boars