2 dependencies in the same task
 

How can I create FF and SS between same pair of tasks. When I add FF then SS will gone. Vice Versa.

To make it clearer, I need Ladder dependency type

This isn't directly possible. One work-around would be to create an intermediate milestone. So as an example, for the start dependency you'd go A->C->B, and for the end dependency you could go straight from A->B.