N.H.
I just had to write to let you know you are not alone. My son is going to be three this summer. He is not a talker and has some unusual tendencies that have raised some red flags about Autism as a possibility. We too are overwhelmed with all the information that we are reading about what this might mean for us.
He has been receiving speech therapy through First Steps but when he turns three he will transition to the local school system for service. He will be evaluated for his needs this week by the school psychologist/therapists etc. but they have only allowed 1 hour for this whole process, which in my opinion can't possibly give them a complete picture of all my son's abilities. But these people are supposed to be professionals so I am trying to give them some credit.
If your sons do not have any identified delays other than speech, maybe you don't have to worry so much. Many people have told me stories about friends/relatives who didn't speak until they were 4 or older.
You seem to be doing everything you can to make sure your boys have what they need in many ways.
Don't be so hard on yourself. You are a good mom. You aren't going to miss the window of opportunity, because this is the window and you are doing everything right. Talking to them and encouraging their responses, even if they are unintelligible right now is the best thing you can do. Also make sure you spend a lot of time narrating everything you are doing. That is what we were told to do from very early on in this.
We are in a position that we are able to also have our son evalutated at Riley Hospital for Children, but that is completely of our own doing. We just decided that it would be better to overreact now, instead of pretending that nothing was wrong and then finding out later that we were in denial. But since you have had your boys evaluated and they do not seem to be having other delays, I don't think you need to worry so much. There are very specific things that these professionals look for, and they must not be exhibiting them.
I really feel for you and wish you the best. Spend the summer enjoying your children and giving them every experience you can, narrating everything you do and see. They will probably begin to speak on their own, but if not you can push for the services they need this fall. If you have friends or relatives who spend much time with your twins, encourage them to talk as much as possible. The narrating seems strange at first, but you just get used to hearing yourself talk. It helps when others are doing it too. Plus, like you said, sometimes when it doesn't come from mom it helps a little.
Best of Luck!