Do you have Dual breakers? otherwise, the 50A is perfect for the Electric Range. You will need two 40A for the Hot water heaters. You will want to wire them according to this (Single phase i am guessing)
http://tankless-water-heaters.com/im...ngle-phase.jpg (figure it is not tank-less but the circuit still should apply). Out of the two breakers, you will want a Red and Black wire. Connect the White wire to the neutral in your breaker box (and ground to earth ground).