Welcome! Much of what you say is very familiar around here; glad you found us. Here are a few comments:
I have not had him tested yet but I think that might be a good idea. Would LOVE some suggestions about testing since I am completely new to this.
I think the majority view here is likely to be not to test until there is some definite reason for doing so. It's expensive; with such young children it's a bit hit and miss (you'll be less likely to get anomolous results because of a kid having a weird day, if you can leave it until they are 6 or so); and many teachers etc. don't really trust testing done on children so young, so you might well find testing done now not very useful for advocacy. If you find that you will need a test to persuade people to accept one of your DSs into a classroom you think is right for him, that would be a reason to do it. It's very good to hear that your older DS is so well placed at the moment, though!
Ah - by the way, the usual convention here is to write DS<age in years> rather than DS<birth order>, i.e. most people would refer to your older DS as "DS3".
He writes on the computer in full sentences like a diary of his day. He is now up to 11,000 words.
You mean, he's typed 11,000 words on the computer? Not such bad fine motor skills there then, actually... Seriously, not many kids that age would do that, and it will make many things easier for your DS that he can.
DS1 is extremely sensitive to noise and VERY emotionally mature. Is this something you find is normal for gifted kids?
This seems a rather odd sentence - I wouldn't normally associate sensitivity to noise with emotional maturity. Do you mean that he is a quiet little boy, perceived as mature because of it? Or is it possible you meant emotionally immature?
You might want to google "Dabrowski's overexcitabilities" which is a term covering the many ways in which gifted children can be intense. Both extreme emotional maturity (relative to age peers) and extreme emotional immaturity (relative to academic skill level) are common in gifted children. Sometimes even in the same kid :-/
