Hi Karen, my boys are just a bit younger than your pair. I'm not sure who is the leader with speech, exactly, but they do seem to have the exact same vocabulary. They pronounce "sister" differently (one says "dit-duh" and one says "zhi-ser" and sometime even seems to get a "t" in there for the diphthong, amazingly enough, and the initial consonant is sounding more and more like an S. I swear, it seems like instead of building a vocabulary, he is just perfecting this one challenging word bit by bit over the months
They pretty much have a limited vocabulary. Just words (names) for all of us in the family, the same name for each other (Nana--sounds like NahNah) but if I ask a boy to say his twin's name, he'll say Nana, and if I ask him to say his own name, he'll say Nana while pointing to his own chest, like the self-indication is part of saying "his" name (which is just Nana. I'm not sure if they are saying a NAME/their NAMES, or if it's some kind of word that means "them" somehow, or what.) I think Nana may have originated as an approximation of "Noel," and then got used for both names for whatever reason. I think Noel USED to say "LaNah" for Linus and then "NahNah" for Noel, but the matching syllable stayed.
They have just recently been adding some initial consonant sounds ("Beeee----s" for "beans", "caaaaaah" for "car," etc.) and final consonant sounds (a clicking "K" sound that doesn't sound phonetically like "kuh" but sounds just like the short, click of the final consonant of "creek," and for them it means "creek"
Otherwise, they are not adding that much yet. But they still have lots of signs, plus a lot of "sound" or audible signs (mostly animal sounds to MEAN the animals themselves--not just to answer the question of "what does a cat say?", but some of their "audible" signs are for things like "wind" or "fan." And some of those are in combination with hand signs, too.)
The other thing is they've just begun pairing words together. This is definitely a matter of spoken word with sign, not two spoken words so far. And they tend to copy or duplicate what the brother does, so they both pick up the little "sentences."
So far it's been pairings like:
They also distinguish between hi and goodbye (wave differently to signify each word) and they've started requesting additional signs. Like "library" (where their dad works), "angry," "mad," "don't." (I suggested that I look up ASL signs for those, and they were VERY into that, nodding deeply. Then I'd suggest other words and they'd show me their own signs for those particular words, like "Not necessary, I can already say that." These were signs they'd made up for "happy" and "rain" and "stop"; it's like an elaborate game of charades over here. They were showing me that "joy" is basically pulling themselves straight up on the bed, then leaning forward without putting out their arms until they fall fully on their faces. Every time I mentioned the word "joy," they'd clap their hands and then gather themselves so tall and do the free fall, flat out. Hilarious. Thank goodness they only seem to sign "joy" in this way on the bed.