When I last had to do this, I 'solved' it by using 'vsx_provisioning_tool show vd', but that's not great - it requires comms to the firewalls, one at a time and is very slow. So....
How does one, in script/API, find member VS of a VSX host? Or, conversely, given a member VS, how do you find its parent? Assuming you know an objId, you show the generic-object.... and none of the fields seem to give you any clue about the relationships.
I'm using MDS, btw, so it's a little complicated by wondering which domain or global these might be stored in.