Well, how old are they, and how much DO they weigh?
They should be at least 1500 grams.

Have you done anything to cycle them (and the males) for breeding? (IE, any light or temp adjustments, etc).
When have you started breeding attempts?

In most cases, ball pythons will breed November through April, sometimes even into May. This probably has to do with autumn storms being followed by an extended dry period, and then spring storms initiate egg laying.

I use natural light through the windows. I used to cool, but I didn't cool this year, and my results are just as good.

If you're trying to breed them out of season, that could be why they're not going. At this point, while I do have a couple of females still locking with a male, most of my females are done with the males, and are gravid and preparing to lay eggs soon--some have reabsorbed follicles and are refusing the males, and will probably start eating again soon.
Breeding season is almost over.