You can’t have female piggies anywhere near your boys if you wish your boys to remain together. You certainly can’t put sows in the same cage as two boys. Just having a sow in the same room and your boys smelling a sow
will cause your boys to fight with each other and will ruin your boys relationship.
If you really want sows, then you would have to neuter your boys, have a six week wait after the operation for them to become infertile, split them up and put them in separate cages with a suitable character compatible sow each.
Or, you get another pair of boars and keep them in a separate cage to your current boar pair. So you have two separate boar pairs
Spaying sows is a major operation for them. Generally it’s not done as routine, but instead as a medical need. If you know a rescue who routinely does it then that is fine, but you still can’t put sows, spayed or not, in with or even in the same room as, your boys if you wish your boys to be able to stay living together.