The vase on the divider next to Dr. Higgins in the restaurant scene moves from being centered on the intersection of the "T" to having the edge of the base on the "T" and back to being centered on the "T".
There is no evidence that Van Gogh had any children, hence he would not have grandchildren.
It has been proven that names were not changed at Ellis Island. The ship manifests were filled out in the country of origin so not speaking English would not have been an issue. Plus they had, and used, translators at Ellis Island.
Multiple characters in this movie are art experts and would know that Vincent Van Gogh did not have any children and therefore should have questioned the validity of Harper's claim that the new artist was Van Gogh's direct descendant.