I've tried two females in a 5 gallon for a brief period, and they got along for about 3 days, before the less dominant one had her back fin ripped. - In a larger tank - ie - 10 gal. plus - add lots of floating plants - and you can have 3+ bettas. And, yes, I will recommend - add the cories - they are great enthusiastic swimmers who will keep the betta girls so entertained that some of the territorialism will dissapate. IT won't be 100% gone - I have a 20 gal with 5 girls and 3 cories - and I still see a bit of chasing - But with those floaters _ for me, I have a huge - plant with lots of hanging roots and branches/leaves - so that the others can always go into hiding, and there's enough girls in there that there isn't any 'one' being picked on more than the rest.
keeping 2 girls alone can be much more difficult because the one fish will always dominate the other ...
good luck.