Can we declare static and instance block inside an Interface in Java?

No, Mainly, static blocks are used to initialize the class/static variables if you have not initialized them at the time of declaration.
In case of interfaces when you declare a field in it. It is mandatory to assign value to it else, a compile time error is generated.

Interfaces do not allow static blocks but do allow public final static member. If someone wants to initialize the variable based on some logic, it is not possible in interfaces but possible in classes.