Assuming that the rule "(x, y)" means that both coordinates are multiplied by some factor x and y respectively, the rules that follow the Grump family's rule are:
(3x, 3y)
(2x, y)
(x, 4y)
(4x, 4y)
The rules that do not follow the Grump family's rule are:
(6x, 5y)
(9x, 9y)
(0.3x, 0.3y)
Therefore, the family members that follow Mr. Grump's rule are in red, and the imposters that don't follow the rule are in blue:
Red: (3x, 3y), (2x, y), (x, 4y), (4x, 4y)
Blue: (6x, 5y), (9x, 9y), (0.3x, 0.3y)