
How often does she cycle because fact is she just might be coming into season again. I had one who cycled every 5 months (mine generally came in every 8 months, and she was 'family' so this was abnormal) and as she wasn't really up to standard anyway, I had her spayed to stop all that.
The male puppies won't normally be viable much before 7 months, but again, each is different. What ISn't a good idea is to castrate before a year, by which time the growth plates should have closed. And why have 2 male brothers in any case. With an entire bitch on the property, you could end up with some fighting when she does come into season, unless you make arrangements for her, or the boys to be elsewhere during her season. Hardly ideal.
Lastly, if these boys are only puppies, with some developing yet to happen, how do you know that by the time they are mature and ready to mate, they will still be 'right' for your bitch, bloodlines and common faults? I think, if breeding is on your agenda, you'd have been far better advised to use a suitable outside stud dog. So now you have 3 dogs, and a rapidly expanding number of dogs if you intend to keep something from any planned litter!
I have no idea why what's going on otherwise, is going on, but YOU need to be in charge of their activities and prevent/avoid.