How can I specify a unique form to use for object editing from each query?
There are a couple of ways you could do it:
1) Have the query use 2 different Operations for editing. Each operation would have a different applicability condition. This will allow the appropriate link to show up beside each of your 2 member types. Each operation would also have a seperate "use this form" specified.
2) You could have 1 Operation that runs a process which has an IF condition. If the member type is A, then you want to edit the object using form A. Otherwise edit it for Form B.
I tried using the "Use Form" option in the query editor but that seems to nullify the selection criteria ....
As you found out, when you click "Use Form" in a query, you can not also have other selection criteria. I agree that this would be a useful feature.
