If you have access to the Combine Surfaces Command, you can combine multiple "Part Surfaces (that are islands that do not overlap) into a single surface containing multiple islands, and then you can merge that with another surface in one command. This depends on the source surfaces being separate and non overlapping, but it does work well in certain scenarios.
If the surfaces overlap, then you have to determine the order and priority in which you want to merge the surfaces and then merge the surfaces together gradually one by one.
I did make a post on this in the last couple of weeks - I will send you the link shortly.
Alan