I have Six Two week old kittens, 2 of them are smaller and seem to be slower at walking/learning?

Are these kittens dying thier both orange twins the boy is just about as big as the other 4 while the girl seems to be the runt?, they are both eating each feeding session , we are gonna take them to the vet once we have the extra money, im just nervous because I have been wanting a orange cat soo long I need garfield :(, the boy also can walk just as good as the rest just not as big, please cat owners help.me out Please