Can 2 male cousins and 1 female
cousin ( all three are cousins)
sleep in a hotel apartment that’s has 1 bedroom with two beds for the boys and a living room with 1 sofa bed for the girl
They are singles ages 19-21.
Such a situation is yichud. This is because at night there is a need for a third male in order to prevent yichud. In addition, there is another factor here, that the three cousins are friendly with each other, which makes the halachos of yichud stricter.
Hashem should help you find some other option.