What is the capability of AVRISP and USBASP on ATMega48, 328, 2560?
Yes.
Yes.
Depends on the specific hardware. See the documentation for the exact variant you have.
See 3.
No. They have their own protocol that you must use instead. They are selectable from the Programmer menu in the IDE though. However, you must unprogram the fuse bits outside of the IDE.
No. They are low-cost tools meant to be used for programming only. You will need an Atmel-supplied debugger in order to use Atmel Studio's debugging features.