Something apparent lately to me during therapies is how much the boys problem solve together. One holds the bucket so the other can take things out; one arranges the couch cushion off the couch so the other can climb up, if one is sad there is always a hand from the other rubbing his head, etc. Most notably, they talk some type of jibber-jabber (twin speak) and seem to be happy with the meaning of it. Their smiles seem to mean they understand.
They don't use sign language to talk to each other, rather their sign language is only directed to Mom and Dad or Hannah and Nate. But through their wonderful teachers at Promise and our speech therapist, we will soon get the boys using words. Super twin powers will continue, but hopefully so will "words" and more signs.