One may just be infertile. Does the female even go into heat?

I would really change your food mixture. Hamster food is nowhere near what rats need, and it's definitely not helping. Dog food should be fed in small quantities, and it should be very high quality dog food(not the cheap junk from the grocery store). Grains, cereals, pasta, oatmeal, etc should be their main diet plus lab blocks to make sure they are getting everything they need.

And honestly, I would get them a bigger cage. Air flow can't be that great in a cage the size of a 10-gallon, and I'm sure their lungs are suffering because of it. Male rats produce ALOT of urine, which then produces alot of ammonia. High levels of ammonia cause lung scarring and other internal problems, so a wire mesh cage(made for rats or other small animals) would be best. It needs to have a solid bottom, and either solid or small wire mesh shelves. The suggested space for rats is 1-2sq ft of space.