Not a good idea, if the chin ends up female. The two males could fight to the death over her, and even if they somehow didn't, trying to intro a third to any pair could result in the original pair breaking up and not getting along. So, even if it's a male, be careful if you want to introduce it to your current boys (after quarantine, of course).
Not to mention, if it is a female, then you could end up with babies, which, if it goes wrong, can end up killing the female. I had a rescue come in once that was pregnant, and she was so small when she delivered, the babies literally ripped their way out, causing internal bleeding... tried to spay her to stop the bleeding, she lived through the surgery, but not through the night. And that was an $800 expense for a chin that didn't make it. And all the babies had neurological problems and died shortly after. Lots of people think babies are all cuddly and rainbows, but problems do come up and things do go wrong.