Agreed. I know it’s tempting to “save” bettas from their cups remember those are always meant to be temporary holding. You’re creating a permanent home.
Aqadvisor may be right that your tank can handle the bioload of that number of fish but that doesn’t take into account that bettas don’t like neighbors of their own species and some have issues with tankmates in general. Crowding bettas with tankmates is not a great idea.
If you want some more activity in the tank you might see if your lfs
has some larger ghost shrimp. Again this may or may not work but I have had larger ghost shrimp with bettas in community tanks that did fine ( until I left on vacation and betta got hungry.... I’d always come home to one less shrimp......)