If they were both 75 ampers at double the voltage then at the same full power, output would be 75 amps--37.5 amps each?
NO
it would be 75 amps at 28.8v etc..
provided the 24v bank could accept 75amps
just like solar panels, current stays the same as the smallest 'supplier' can pass, the voltage is double
75*28, not 37.5 * 28
if (2) batteries can accept 50amps each in parallel AKA 100*12, 50*12*2=1200w,
then they will accept 50amps in series
50*24=1200w
the charging configuration becomes very much like solar panels
you need chargers that have matching operating stats
same voltage and same current
i would not stack two different converters in series, except in a 'make do' situation, using needing higher voltage and LOWER amps
if changing systems, then start over with matching converters
designed for the job