OK, some more basic information about permissions B and C:

B is a residence permit for one year. There are several different reasons to get a B, and there are as well different purposes to be fulfilled by the residence. A B permit has to be renewed every year, and the reasons and purposes are verified with every application for prolongation of the permit.
I won't go into the details of the various reasons and purposes for a B permit. It may become complicated, and as always the practice varies from canton to canton.

C is a permanent and unconditional permit. The paper itself has a validity of 3 years. This limitation and the process of prolongation has only one purpose: To check whether the holder still lives in Switzerland. However, the original reasons for giving a C permit are not verified again.

A C permit can be cancelled for the following reasons:
- No application for prolongation
- Residence out of Switzerland for at least 6 months
- Eviction order following a conviction or debts

To come back to our example: For obtaining the C permit it is a condition to stay with the parent who has already a C permit. But it is no condition to keep the permit.

Or to give a different example: Many Italians living here are born here, maybe their parents returned back south or died. They still have the Italian nationality and a C permit. As long as they don't become criminals, this situation may remain for generations.