A 10 gallon tank is the bare minimum for putting females together. Even then, there should be no less than 4 occupying the tank at a time. Even though they are capable of co-existing together, they can potentially be as aggressive as their male counterparts. So it is important to spread out the aggression by having 4 or more.
As for the one gallon, as everyone else has said, one betta is the maximum. Sometimes depending on the size of the fish, even that can be too small. A lot of members of this forum will recommend a 2 gallon tank or higher to keep a betta comfortable.
Anyway, welcome to the forum! If you have any more questions, feel free to let us know! :)