My oldest wore a pull-up to bed every night (and soaked it) until just before her 4th birthday. (She did stay dry for naps.)
A couple days before her 4th birthday, she told me that she didn't want to wear diapers to bed anymore, so we decided to let her try wearing undies. We spent several months with lots of wet beds and going back and forth from diapers to undies. We also bought two of those mattress protectors that lie on top of the sheet (right under the child's middle) so that we only had to change that and the child's clothes in case of an accident. The rest of the bed stayed dry.
Because my daughter was so insistent about wanting to wear undies to bed and because she was making some progress (wetting fewer and fewer times per week), we let her keep trying. It took a few months before she was consistently dry at night. Even now at age 5 1/2, she's more likely to have an occasional accident at night (once every couple months or so) than her 4-year-old sister.
Anyway, I just wanted to share my story because I'm not sure if wearing underwear to bed made a difference or not, but it was something my daughter wanted to do, and it was a long process, but we worked through it. If your boys are interested, it might be worth trying. If not, they might not be ready yet.
Edited to add that my daughter was consistently staying dry for naps before we quit making her wear a naptime diaper. It was overnight that we had the biggest problem with.