I met my two friends.

Hi teachers!

I have been taught that two determines cannot be used together as in #1.

However I came across many sentences such as #2 #3, #4, and #5. Can you please tell me whether these are grammatical?

1. This is a my book. (X)

2 These are my some books (?)

3. I met his many friends (?)

4. His two sons are doctors (?)

5. Her a few challenges have been successful. (?)

Many thanks teachers ??