Bickering is normal at first. That may be a little more aggressive than I usually see if they're doing it constantly. Sometimes it's more timid. Just make sure they aren't locking jaws. If they do, you need to separate them. They appear to be almost the same size, which is bad, so I would watch very closely.
I had two that were pretty much the same size because I couldn't find any with a big size difference. They were fighting like yours and I came home to this
We removed the healthier one, and kept the beat up one. It actually healed completely, is now the female of a different pair (sans tail) and just started to lay eggs.