posvađati

1. (posvađati se) to quarrel; to fall out
   Posvađao sam se s bratom oko nasledstva. — I fell out with my brother over the inheritance.
   Opet su se posvađali zbog sitnice. — They quarrelled over a trifle again.
2. (+ acc.) to set at odds; to turn against each other
   Ta glupa priča ih je posvađala. — That stupid story set them against each other.

With whom is s(a) + instrumental; over what is oko/zbog + genitive.