Just so you know, I trust local breeders on keeping their bettas healthy - because they may suffer big losses if they don't. . . . I'm talking about losing hundreds of bettas. The only thing I'm never sure of is that many of these breeders keep their bettas in slightly salted water which is actually bad for them in the long run. In short, I hardly ever quarantine unless shipping takes more than 2 days (water prams will be bad). Slow acclimation will suffice.
This is just me. I'm not saying this is the correct way of doing it.
The purpose of quarantine is to reduce or eliminate possible disease spreading. Your females have been in quarantine for 3 weeks and show no infection, thus it is safe to say that they are free from diseases. If by chance they get sick later, it is due to a new infection or caught from the new tank (their new home). Quarantine time does not restart after each shipment - specially when they go through : quarantine - ship - quarantine . . . .
Remember, if the females are now in their own solitary, they will fight for dominance once placed in one tank. Each bite MIGHT cause infection. So IMO it would be best to put them together now while you can monitor them and medicate if needed, rather than later and you can't monitor them at all.
looks like it is in the right section :) you might want to ask some breeders who actually import fish, as they will be more experience with these types of situations. I'm not ery familiar with the members in betta breeding, however Indjo should be able to point you in the right direction :)