The fact that your two youngest are going in and out of season could be contributing to your females issues with them, as she cant be the dominate one, as in the proper hierarchy, they are above her. You also have health risks to your younger two, the pill isn't a good option for cats, and you could actually be making them infertile by using it, the majority of breeders wont use it, as there are no guarantees they can breed from them after having them on it. So, if you are considering breeding, you should do all the thinking before buying potential breeding cats, as it isn't good on their health to be waiting until you decide to breed from them.