The older brother made a trip to Moscow and probably went to Chechnya and got military training with some splinter group. I think the younger brother was mostly tagging along. The older brother sounds like a radical nut. This is just my guess based on what they found so far. I just can't imagine homegrown american kids figured out how to master IEDs. Remember that they have many, and used them effectively - it wasn't a "good how to make bombs" ordeal. Somebody had to have hands on learning.