I've been trying to infect our youth with a vision for RMNP for years. Props to yours wanting to give it a go.
My brother is a hike-master there during the summer. He took me on a few hikes in both RMNP and Arapaho. He's not a fan of backpacking, but one day I think we'll get it together.
Personally, I find an insertion into the Wild Basin from near Allenspark very appealing. But not having done any of this with scouts, I'll not give any specific advice. Just, some general points on planning:
First: required reading for you and your scouts: https://www.nps.gov/...ess-camping.htm
Second, you need plans A, B, and C for any of this.
Third, just like Philmont, start your boys on the hike-a-month club so that they are comfortable with all their gear by departure.