1) Arguing 2) Battling 3) Butting heads 4) Clashing 5) Conflicting 6) Contentious 7) Contradictory 8) Differing 9) Disagreeing 10) Disagreeing like bookies 11) Discordant 12) Engaged in sibling rivalry 13) Fighting 14) In conflict 15) In disagreement 16) Like bitter rivals 17) Not getting along 18) Not on the best of terms