Dear LG,
My oldest two sons are in middle school (6th and 8th grades) and close in abilities. I let my oldest son try things first (guinea pig) and then try it on the next. For math, I've signed up for EPGY distance course for the oldest. He can try it for 3 months and then I can sign up the younger son. My oldest son has no one in his class to motivate him to learn as rapidly as he can, and he actually asked for this course, saying the last two years of math have been a waste (Moms just love hearing that, don't we? Especially when we think we're so intuned with all their educational needs, but they have failed to mention they've been coasting). I thought my younger son needed a little adjust time (new school, new curriculum) before adding a distance course, but in my mind they could inspire each other when he does start EPGY.
If my older son likes this distance learning thing, I think I'll incorporate it into his IEP so that he doesn't have to "waste" more time sitting through class, but can work online at that time (instead of doing extra at home).

Sibling rivalry is very tough though, and I think it's destructive to their relationship. I haven't figured out how to handle it with 2 of my other sons, except to keep them separate. They might be working on the same level math, but as long as the older one is always a few objectives ahead, it's been ok. The younger one who can work faster, deliberately does not because he doesn't want to catch up to his brother. I suggested he might want to skip more grades, but he immediately declined, saying, "I need to always be 2 grades behind [brother]," giving me a knowing look. Pretty astute for a 7 yr old.