Predecessors' rhymes with:
assessors, assessors, successors, aggressors, assessors, bresser's, compressors, dresser's, dressers, guessers, lessors, messrs, messrs., mssrs, mssrs., oppressors, presser's, professor's, professors, professors', stressors, successors
Predecessors' sounds like:
predecessor's, predecessors, pritzkers, producer's, producers, producers'