You could certainly run brighter lights! Low light requirements mean just that, they require low lights but any plant will grow in a High Lighting situation. My Anubias flourishes under my fluorescent bulbs!
As for plants here are some to consider:
Java Fern (low light, medium grower)
Java Moss (low light, fast growing)
Anubias (low light, medium grower)
Common Crypts (low-med. light, medium grower)
Anacharis (low light, extremely fast growing)
Hornwort (low light, fast growing)
Moneywort (low light, med-fast growth)
Pennywort (medium light, med-fast growth)
Water Sprite (low light, fast growth)
Water wisteria (low light, fast growth)
So of these plants I highly suggest floating water sprite for any Betta's, especially a sorority since they will spend lots of time up at the top, it breaks up their views of each other and helps block when chasing begins. They also sleep in it.
Hornwort and Anacharis are sometimes finicky but both can be floated or planted. Anacharis is generally a cold water plant but can be acclimated to higher temps like 80*. Grows like a weed too.
So for amounts of plants, I would suggest getting plenty that will grow tall like Anacharis, Hornwort, Water wisteria and water sprite. And then put some Java Ferns and Anubias between them so you're blocking most area's for the girls. You might also be able to get away with Amazon swords which are great for sororites because the leaves get so big and they grow tall. And with an NPT they should do just fine because they are heavy root feeders.