You could use 1 common injector to regulate 2 turbos with 2 Y pieces.

However if 1 turbo starts to fail and reduces its boost output, this will cause the other turbo to be over worked as the injector will compensate (if closed loop). Also it could be difficult to match the 2 turbos outputs. For them to be matched properly you would need each turbo to feed a seperate inlet manifold/plenum each and then control boost pressure outputs from each with 2 air to air injectors.

If your ECU has the facility to monitor turbine/compressor wheel speed then you could also control it that way.