Two transistor flybacks are very common for high input volts/ wide range inputs (similarly for 2 xtor forward), usually a gate drive transformer is used to turn the xtors on and off simultaneously, Regards, Orson Cart.
Thank you for pointing to the LM5015 example. I admit, that I wasn't aware of the two-transistor series circuit used for flyback converters, although some advantages are obvious. Wide range operation seems to be limited compared to the standard single switch flyback topology, however.
For the driver problem, I think that a combination of a standard current mode controller with a bootstrap high-side gate driver should work.
Unfortunately when you look at the detail of the 2 sw f/back operation - std bootstrap is not possible for the high side device as when the bottom device is on - so is the high side - when both devices turn off there are substantial volts across the high side device (& the low side) either way there is no gnd reference to allow a charge of a bootstrap cap.
2 sw f/back is often used with 600V or 800V mosfets for aux supplies off a rectified 3 phase line (565 - 750VDC) where a single switch 1kV mosfet would be a bit short of volt headroom (also the lower volt devices are cheaper) - Regards, Orson Cart.
At least in operation, the bootstrap capacitor should be charged during diode conduction time. But I agree, that an auxilary circuit to precharge the bootstrap capacitor can be required. I assume, that activating the low side switch without the HS would be sufficient in most cases.
I didn't talk about intrinsic diodes rather than the primary clamping diodes. They can be expected to conduct due to leakage inductance, even if the transformed output flyback voltage is considerably lower than the bus voltage.
A more general approach to force recharging of the bootstrap capacitor would be to introduce a lead time in activating the low side switch.
If you have clamp diodes from the primary Tx ends to the rails they need to be properly ON for a certain time (~1uS or possibly more) each cycle to keep the bootstrap cap sufficiently charged - at low output power or low output volts (e.g. under current limit) you would need a fair bit of leakage in the Tx to ensure this (requiring big snubbers on the o/p diodes at full power), also such clamp diodes can only be used where you have fixed maximum o/p voltage and a fairly narrow range of input volts - otherwise the primary clamp voltage (the input rail) will limit the max o/p volts available - and considerable power will cycle between the Tx and the input bus.
Usually a 2 switch is used where it is desirable to have voltage sharing across the devices - which means it may not be possible to turn one on first - Regards, Orson Cart.