Hello Nikunja Maharana,

For Overriding the unlink method, please refer to this link

Link: https://www.odoo.com/forum/help-1/question/how-to-override-only-the-unlink-method-of-account-invoice-class-73910

Make sure before you need to inherit the function or override.

I hope maybe inherit is enough for your case.

If you are overriding the original method rather than extending it, then you can avoid inheriting it and go with overriding.

Anyway for inheriting check this code:

@api.multi
def unlink(self):
    # "your code"
    return super(YourClass, self).unlink()

In both cases, you can check self contains multiple records or not.

Thanks & Regards

Avinash N K