Firstly, before you attempt ANY breeding, PLEASE RESEARCH IT PROPERLY. Breeding betta fish is NOT easy and you WILL require a lot of preparation before you can actually attempt to breed bettas. Otherwise you will surely fail and kill hundreds of baby fry.
Are you keeping them together or are you keeping them separate? If you're keeping them together, they could be nipping at one another, destroying their fins.
If they are being kept apart, they could possibly have fin rot. In which case I would recommend treating with Salt baths/Salt dips.
Salt baths = dissolve 1tsp of AQUARIUM SALT per gallon of tank water. They stay in this. This will promote fin healing.
Salt Dip = 2-3 tsp of AQUARIUM SALT per gallon. take a separate container and make sure the salt dip water is the same temperatures as the regular tank water. Scoop the fish out and put them into the salt dip and let them stay in it for about 5 minutes in this concentrated water.
Afterwards, pour about 2/3 of the salt dip water out and add back the 2/3 of water in REGULAR TANK WATER and let them sit in it for 15 minutes. This will dilute the salt dip so when you put them back into their regular tank, the can adjust to the water conditions a little bit easier.
Sometimes bettas are sensitive to salt dips and will go unconscious (they will roll to their side and you will see slow gill movement), if this happens, just put them back into their regular tank.
Anyhow, salt dips can be preformed at least 5 times per day with at least a 1 hour break in between.
You HAVE to use Aquarium salt. Table salt will kill them.
If you don't see an improvement in 2-3 days, then try Maracyn + Maracyn-two combination. Follow the instructions carefully. If those don't work, you may try other medicines such as Tetracycline, Ampicillin, Maracyn-Plus or Trisulfa.
But please try using salt baths/dips first, because once you start using medicine, the bacteria that is causing the fin rot will start growing immune to the medicine. The longer you use treat your fish, the more likely your fish's immunity to the disease will decrease. In which case you will have to buy fish vitamins to try and help boost it again.