It is already the fact that after the divorce the father scores on the children only that his parents begin to consider grandchildren as ex.

my ex-wife with my ex-wife on my modest requests for help (the former did not pay alimony - business, car, young woman) stated - you are guilty that he left, deal with your son yourself.

Ten years have passed, now grandmother and grandfather are tearfully asking their grandson to come to them, then complain about him to his father, who was not interested in them, then threaten to take my son to court...
Only their grandson does not rush to attend something, although I do not prohibit it, is limited to polite and dry congratulations on the phone on holidays. In visit, he goes to the parents of his father, who are not related to his blood, but love him as a relative and always helped him.

God is your judge and no one else.