lighting halogen 110VAC transformers to 12 VAC, 150W
Your scheme has enough potential problems that I would not recommend it.


Connecting the two transformer primary windings in SERIES is not recommended where the loads (on the secondary side) are DIFFERENT. It means that the power will NOT be equally divided between the two transformers. This will cause the voltage across one of the circuits to be too high and will put the bulb(s) at risk of burning out.
The major problem with operating 60 Hz transformers on 50 Hz is HEAT, not HUM. It is possible to design transformers with enough margin to handle both 50 Hz and 60 Hz. But products designed for a 60Hz market are frequently fitted with power transformers built to a narrow budget margin that causes overheating when operated at 50 Hz.