I think the guppies will be okay. If there are baby guppies, the betta will eat them but I think the adult guppies will be okay. Cinder, just watch to be sure the betta isn’t nipping at the fins of the guppies. Also, try to feed some frozen, thawed blood worms on occasion, sparingly. The betta will like the ‘meatiness’ better than fish or pellet fish food and will satisfy him better so he won’t be staring at the guppies. That is totally disgusting. Cleaning it out would make me vomit.