My understanding, and I certainly hope some of the genetic gurus will weigh in, is that the difference between a single barred male and a double barred male is the double barred male is lighter. If you have both single and double barred males then they came from single barred stock. If a cock is double barred and the hen is barred then the offspring males should all be double barred, which would be the lighter color.
I would not bank trusting that your stock came from a double barred RB given that most of the original stock (if not all) came from GFF and as many on this thread can attest to there are issues with some of GFF Rhodebars not being pure.
If you keep and use your dark males, and they are indeed single barred, then you are 1 step behind working towards pure Rhodebars. If you keep and use your lighter males then you will be 1 step ahead.
If I had both light and darker males I would take the presumption that the light males are double barred and the darker males are single barred. I would concentrate on getting pure Rhodebars (double barred males) and work on darkening the color using your HRIR stock.
Penny