We are starting off with a 220 volt, 200 amp, 1 phase line.
The siren we seek to power has three separate motors.
Motor 1 is a 7hp
Motor 2 is a 4.5hp
Motor 3 is a 1.5hp
RLA is 89amps, 220 volt, 3 phase

I don't know where you came up with 50hp requirement. The motors
themselves only add to 13hp. FOS of 2 only gives you 26 hp. There are
other mitigating factors, but 50hp seems extraordinally over sized.

In any case, is it possible to change the motors out? None of these
are too big to not be used as single phase motors. The biggest factor
would be the mounting type. If you weren't so far away, I could
probably give you at least one of each size, but shipping from my
location would be cheaper to go buy a new one or close to it.

JW