pelearse

At the same time, they are often prone to arguing and even fighting with each other.

infinitive of pelear combined with se

(intransitive) to fight (to contend in physical conflict)
(intransitive) to fight, to argue
(intransitive) to fight for, to struggle against
(reflexive) to mutually fight
(broadly, reflexive) to discord or dispute; to become enemies
(broadly, reflexive) to lose or stop, temporally or definitively, a friendship, partnership, etc.