Sure I can help...Ali is a diabetic, Jack is not. Ali loves to eat. Especially Jack's wet food. What we do to make sure that Ali doesn't eat Jack's food:

1)don't free feed the cats. feed them once in the morning and once in the evening.

2) put the food away after they are done eating. That way Ali doesn't eat Jack's food and Jack doesn't eat Ali's food.

3) feed them in seperate areas/rooms. Ali get's fed on one side of the kitchen and Jack gets fed on the other.

This doesn't mean that Ali still doesn't try to eat Jack's food, so I really have to watch her.

Hope this can help your friend.