Welcome to Fishlore. It's awesome that your girls are getting along. Dave (BettaCouple) is right that this isn't very much room for them to swim, though.
It's amazing the difference that a larger tank can make on the coloring/attitude of a fish. We've had so many people who had been keeping their bettas in bowls (because that's what pet stores tell them they should do) switch to 5-10g tanks and come back amazed that their bettas have shown so much more personality and brighter colors.
Four things to remember about 99% of the advice around here:
1) It is with the interest of both you and your fish in mind. We want to see everyone's tanks succeed because it makes for happier aquarists, as well as happier fish.
2) It is based on our collective experience (this includes
your experience, now, BTW).
3) It is
not infallible. Despite the fact that it is based on the experience of all of the members, there are exceptions (such as your sorority tank working out for so long) to almost all of the "rules" that we state. Aside from that, since we sometimes disagree on things, not everything we say is necessarily 100% right. (I even sometimes disagree with Dave, who has provided much of the knowledge that I now have)
4) You don't have to abide by it.
Neat Pleco. Those patterns are going to look great as it grows bigger.
Sorry to hear about your goldfish.