Cat eating in other cats food bowl?

i have a 2 himalayan cats that are 2 years old and one of them is not eating from her own food bowl but in the other cats. but the thing is that when she tries to eat from my other cats food bowl, she always gets attacked from the other cat because they are very territorial. so she is losing ALOT of weight, we already made a check up at the vet to.she is very thin while the other cat is fat. we have the same brands and types of food in both the food bowls..wondering why this is happening?????