That's wonderful that your boys have made such huge improvements with early intervention! My son Andrew is 9 and was diagnosed with "severe autism" at age 20 months. With early, intense intervention, his diagnosis was later changed to "mild autism" around age 5-6. He has done great in regular education classrooms every year, beginning with preschool at age 4. He has always had a one-on-one aide assigned to him, which has been key to his success. Another thing that has made a big difference, is that I have been very pro-active in anticipating potential problems before they appear, and taking steps to prevent them. For example, children with autism tend to be misunderstood and therefore bullied or excluded by their peers. So at the beginning of every school year, I meet with the school staff that will be involved with my son (teacher, aide, principal, speech therapist, OT, resource specialist, etc.) to express my concerns and ask them to watch his interactions and let me know how things are going. They are always very willing to do so, you just have to approach it like you are asking them for a favor and that you are so thankful to them for their help, and not like you "expect" it. I always offer to help out at the school as well (making copies, helping with art projects, in the lunchroom, wherever help is needed) which makes the staff much more willing to watch out for my son and be a second set of eyes for me to watch out for him. Every year I also give my son's teacher a book called "My Friend with Autism" by Beverly Bishop for them to share with the class. It really helps the other children understand (at their age level) what autism is, and why my son acts different sometimes, and it also points out that everyone is good at some things and not-so-good at some things. My personal experience is that my son has not been bullied, and has been 100% accepted and included with his typical peers, both in a private Christian school and at our neighborhood public school. He actually is one of the more popular kids, and over the years, 6 or 7 moms have told me that their daughters have cried when they have started a new school year and Andrew wasn't in the same class as them! I go to school at least once a week (to volunteer, but really it's so I can "spy" on my son!) and I always am very pleased with what I see as far as how he is functioning at school. It might ease your mind a little bit if you can be there often and see for yourself how he is doing (I'm sure the staff will have something they can use your help with, so your son won't know you're there to watch him). If you aren't happy with something that you see, you can often times take care of it yourself (along with the staff's help) without needing to have an intervention put into his IEP. Sometimes, it's more serious and you need to get more help for him, but it sounds from what you wrote that he (like my son) is doing really well, and you can just monitor the situation to make sure no behaviors or other issues come up.
Good luck with your boys, and best wishes to you!
A.