Expected power draw for same flyback converters with outputs connected in series?
Connected in series the current through the output of each converter will be equal:
this is a consequence of kirchoff's node law.

If you want more power however you should consider a forward converter topology in preference to the simpler flyback topology. above about 150W a forwards converter is more practical because the transfromer used in a forwards converter is more compact than the one in a flyback.