How old are the boys?
Straightlining all the time might be fun for them for now, but they will not improve that way.
The dynamics of a good group lesson (peer pressure!) could help convince them that turning can be fun. When they are willing to turn they can begin to ski steeper and more challenging terrain. An all day lesson can allow the coach enough time to develop a rapport with the kids, teach them new skills, and allow for guided practice on appropriate terrain. Multiple days in a row can be even more effective.
Other good options to require turning without lecturing: beginner trees and moguls.
I have one strong suggestion for your husband: always set a good example. He should ski the way he wants them to ski. Eventually the boys will ski like he does. If he always turns, even on the easy terrain, they will eventually emulate him.
It may also set a good example for him to take a group lesson. If he shows that he is willing to listen to and learn from coaches, the boys may respect the coaches more.
Excellent point! Thank you so much for that perspective. I guess it’s just the mama in me that makes me want to be close to my boys.This! Waiting in lift lines then riding the lift are when you engage with the people you are with--it's not like you are carrying on conversations while actually in the act of skiing. My husband and I ski at different speeds to mid points or lifts, then ride back up with each other.