Lovely though they are, you should never breed bettas if you aren't certain of their health status, age, and lineage. Assuming you got them from a pet store, not a breeder, I would not go for it. If your pair is too old, the spawn may fail, or may come out malformed. If either is unhealthy, the stress of breeding could be detrimental. And, if you don't know their lineage, you are going to wind up with a bunch of VTs or mixed tail types that will be near impossible to find homes for.