Can my father in law who is a American citizen sponsor his grand kids who are canadian citizens to the USA

A relationship between grandfather and grandchildren is unfortunately not one that can lead to permanent resident sponsorship. Perhaps their grandfather would be satisfied with less, e.g. having the children stay with him during school breaks and the summer. That could be done just by you taking the children to the US on your passports since Canadians do not need visas to cross the border and if need be, explaining your purpose to CBP at the border. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.