"Is it possible to use P3.6 and P3.7 for other purpose such as driving LEDs at the same time when P3.5,P3.0 and P3.1 are used for mentioned function purpose ?"

Why not. It's possible for systems without an external data/address bus. Assure that SW don't generate MOVX ... inctructions.

BTW: Take care about port overloading if you like to drive LEDs.

Vaclav