Question About Eating Habits.

I have two siamese, almost 1 year old, from the same litter...who are really two peas in a pod.....best of friends. Recently my girl has stopped eating with her brother. When i put out dry food she waits for him to finish before she will eat even though they each have food bowls. Same thing with the wet food. We have to place her dish in a different part of the kitchen. It seems strange to us as they do eveything together. When we got them from the breeder they actually ate from one bowl. Is this normal cat behaviour?