You'll probably get much more qualified answers than the one I'm about to give. That's one of the good things about Epic. So, here goes.
Much like you, my family made their first ski trip out west last year for Spring Break. We did SLC resorts for a week. I enrolled my (then) 5 year old and 8 year old in all day ski school for 3 days @ Solitude. I was very pleased with the instruction that they recieved. My 5 yo and 8 yo were never in the same group. Having observed this dynamic, I think it was a good thing that they weren't together. Even if their ski level is/was the same, their maturity level is not the same. BTW, my 8 yo is a girl and my 5 yo is a boy. So take that for what it's worth. My daughter is mature for her age and comfortable with kids who are older than her. She's also very calculating and takes instruction well. In contrast, my son is very naturally athletic, he's rambunctious, and he's a joker. It was better for him to be with other 5 yo kids.
The private lesson is something that I don't have any experience with regarding my children. I've had a private lesson as has my wife, but my kids only did group for the 3 days.
Your kids may be different. The age difference is only two years instead of three and they're both boys.
Good luck. As a parent I know what your intentions are. I wanted my kids to have a very positive first experience so skiing would take hold. And, I don't want to be their teacher. I would get too frustrated and don't have the patience or the skills for it.