I ran into 2 problems.
1/ Whatever condition; de create action (when used with a family) is totaly random.
Problem: you can't create an instance that meets the condition.
2/ The family variables for a newly created family-instance fall back to the values as set in the layout.
Problem: you can't make a condition to test the newly created instance on previous changed family variables.
I made a workaround. But i am not happy with it. It is no advertising for the use of families. Hope you understand my English.