Breeding bettas is no joke. It is a hard and demanding and space consuming job to do it right. I am so sorry to tell you that unless you are getting a breeding pair from a breeder, the chances that the Bettas you buy in your
LFS are too old to breed. I have also read articles stating that the Bettas found in the LFS are not worth breeding as they will never be "fine specimens" (show Bettas). Well, not all of us can afford a breeding pair and I would say that your family members are very lucky to have had a bunch of fry.
Bettas are also prone to do damage on each other post-spawn (mostly the males injuring the females, but the books have stated they do sometimes attack each other.)
Rose