In need of help.

Okay, first off I suck at proper gammer, as i am a computer science major, so sorry. lol also if i'm in the wrong thread just tell me please, since im new to this site.

okay, lets get to it. i have two cats one is named oreo and the other nala. nala is about 18 yrs old, and oreo is about 12, and both are fat. lol nala is a diabetic, so she has to take insulin shots and eats this certain dry food(idk what the name of it is) and gets fed upstairs because she has hard time walking at times. well oreo is a lazy ass so instead of going downstairs to eat, he just eats hers. Now the problem is oreo is my cat so he sleeps with me but since he eats most of nala's food, he throws up in my room, EVERYWHERE at anytime day/night. if you catch my drift.. and he has done this multiple times

so anyways, if anyone has any kind of solution. please let me know. my parents don't really care that he is doing this and its really making me mad. 

You're in the right thread--and the right site!

Did the vet recommend the dry food, is it prescription dry food?  FWIW, most dry food is full of carbs which is contraindicated for diabetics (humans and cats).

Wet food is better than dry food, better nutritionally speaking, and lower in calories.

I would feed them wet food, Fancy Feast Classic is relatively low in carbohydrates which is appropriate for your cat who is diabetic.  There are other higher quality foods, though more expensive.

Regarding Oreo who throws up:  is this new behavior?  He could be reacting to Nala's food.  He could be throwing up because of a medical condition.  Or allergies.  Or stress.  If knew behavior, he should go the vets.  What does your vet say about their weight?

Here is an article about nutrition for cats.

And one about diabetic cats.

And finally about overweight cats.  You probably know that if your cat can lose some weight, he may need less insulin.