You can sponsor your father but a grandson isnt eligible under the PGP program unless he has been adopted. Has he been adopted by your grandfather? Is the grandson (your cousin) an orphan?
If this is to get around the fact that your father failed to declare you in his PR application, then no, this will not work.
You are not classified as your grandfather's dependent. Additionally, since your father failed to declare you, any sort of family sponsorship is unfortunately not going to work out for you.
