I don’t think you mean to be disrespectful, but your comment is a bit ignorant.
I believe both players played for Ireland teams at youth level.
Nationality is not straight forward. Country of birth, where you grew up, where you’ve lived a long time, where you are proud of, where your parents came from … can all play a part.
In football, it’s also about where is your best chance of success.
Grealish and Rice both chose England. Good luck to them, but anyone who saw the excitement of the Jack charlton Era would take a few anglo Irish players of quality over some in the squad now.