the best thing is to go to a rescue where the piggies will be bonded already, you can have 2 girls, which is good if you want to add later, 2 boys also works but you need more room and 2 of everything also its a lot harder to add any more piggies later, they dont have to be brothers.
or you could go for a neutered boy and girl.
its up to you, but i would advise visiting a rescue nearby