Aggression between geckos can happen at any time (even if they have lived together for years). It could just be that one of the females got fed up with the male or one of them is becoming more territorial. Your best bet is just to make sure that the geckos have enough space and that the two with the now missing tails have a clean environment to heal up in.

Most males will still breed with a female that bit/ate his tail unless for some reason the female has become very aggressive or grown much larger than him. I have one particular girl who ate the tail of 2 different males during different breeding seasons and both males continued to breed with her quite well. Tail loss can be a risk associated with breeding, but generally it does not cause any other ill effects as long as everything else is in order (space, diet, etc) .

You definitely only want to keep your male in with your females for part of the year--females will retain sperm and continue laying fertile eggs for 3-6+ months after they are separated. Once the females have laid all of their eggs they need a period of time to rest before being bred again--I give all of my females a minimum of 9 months off between each season to ensure both healthy breeders and babies. Males often need some time off as well, in order to put on some weight and rest (some males do not eat as well while breeding as they tend to just focus on that one thing).