Betta Fish CAN coexist with other fish. However, you'll need to pick your new fish carefully. Anything colorful with flashy fins will cause a problem. Typically you should add fish that are larger...
Well, glo fish are just zebra danios geneticly engeneered. So most fish will go with them. Anything that is not aggressive or a lot bigger than them should be fine.
Any other kind of goldfish can go, however, be cautious about the amount in the tank. Goldfish are hearty, but notoriously sloppy.
The only other kind of fish that would really go with a Goldfish,...