Under 'normal' circumstances, yes, but these unhappily aren't normal, (although becoming so, nowadays.) I wouldn't say anything, but concentrate on maintaining links with your grandchildren.
It would be sensible for your son to make himself known at the school the children will be attending, and ask for notification of forthcoming events such as concerts, plays and parents' evenings, copies of their reports, and also read the school's website. It was mean of your daughter in law not to inform him of their 'graduation', but rather than arguing about it, best to circumvent her with foreknowledge of the dates and times of events, and insist on a fair share.