You are out of synch by two generations. So they would be first cousins twice removed.
First cousins twice removed.
Your first cousin's grandson is your first cousin twice removed.
Your first cousin's grandson is your first cousin, twice removed. Your second cousin's grandson is your second cousin, twice removed.
Your first cousin's grandson son is your grandson's third cousin. Your second cousin's grandson is your grandson's fourth cousin. Etc., etc.
The grandson of your first cousin and your grandson are third cousins to eachother.
Your grandmother's first cousin's grandson is your third cousin.
Your grandson and your first cousin are first cousins, twice removed.
The grandson of your father's first cousin is your second cousin once removed.
Your grandson and your first cousin are first cousins, twice removed. Your grandson and your second cousin are second cousins, twice removed. and so forth.
The grandson of your mother's first cousin is your second cousin, once removed.
Your first cousin's grandson is your first cousin twice removed. Your second cousin's grandson is your second cousin twice removed. Your third cousin's grandson is your third cousin twice removed. And so forth. If your cousin is once removed, twice removed, etc., the relationship possibilities for you and the grandson become more varied and complex.
Your great grandmother's first cousin's grandson is your third cousin once removed
Your great-grandmother's first cousin's grandson is your third cousin once removed.