Killing one is definitely possible if you have the power to do so. The Uvi are extremely vicious and will try to fight back. Unless a character has pretty elevated powers or magic, it's likely they won't come out of the interaction completely unscathed. You could theoretically rip out a soul, but that's something more open to interpretation and canon powers.

Their language is very primitive and based more on physical cues and instinct than verbiage. They have a limited speaking vocabulary that mostly consists of one or two word phrases. "Go," "mine," "move," etc. Nothing too intellectual or complex if you're looking for conversation. This language is reserved solely for their time on the land, though, since they don't have the ability to talk underwater -- thus the need for a more visually represented language instead of a aural one.