How To Bring A Kitten Home To Another Cat?

I have a very cat loving 5 yr old kitten that I rescued from the vets after he had been run over by a car. He was taken to the vet and had stitches put in him for his injuries, antibiotics and pain meds were given him as well. Anyways back to my story…. My parents are going on vacation, leaving me with this little guy and my 3 year old kitten (who is also very protective of her brother). I am trying really hard not to be overly aggressive around them… But they both do fit quite nicely into our living room so we can’t exactly keep them out of it.. They don’t sleep together or even spend alot of time together but when they’re all curled up next to each other its such an adorable sight!! My question is how do you tell your new kitty that she’s now allowed in their space? This will never happen again if i can help it!

Thanks for any advice!!!