Hello,
Are you thinking of replacing T1-T4 with two ADuM32XX ICs (from AD7730 datasheet)?
I believe in this case the ADuM32XX would see 5V from VDD1 to GND1, and should work in this situation. I may be misunderstanding your question, and if so, a schematic might help me, if you are able to supply one.
The inputs and outputs of the ADuM32XX are constrained to be within the VDD and GND rails of their respective isolation region, but I don't think that's what you are asking about.
RSchnell