Let's cut the whole thing into two parts:
1) Orphaned user 'qc'
2) Users not logging to databases
For number 1 I still suggest changing db owner. Change it to what it already is, I thing it is worth trying and for sure it won't hurt.
For number 2 it depends on the users rights, so you can go and fix it the normal way.
Does it make sense?
-- Gianluca Sartori