Is it allowed to use adjective clause inside the other adjective clause?

Question

Original problem:

Understanding and using English Grammar 4th ed. By. B. S. Azar p. 291

Complete the sentences with your own words. Use adjective clauses.

8. In my apartment building, there are twenty apartments, several of __________

I'd like to use "whose" to express something that possessed by twenty apartments. In this case I chose people who live in those apartments.

Then, here's my sentence:

In my apartment building, there are twenty apartments, several of whose people who live in are friends of mine.

Is this sentence grammatically correct?

Answer 1

Your example is unnatural.

To use "whose" to describe what you have specified, you could say

In my apartment building, there are twenty apartments several of whose people living there are friends of mine.