Awwww. Now you've got to call them "Blanket" and "Comforter".
I'm amazed. No cat fights, disagreements or other issues introducing a couple of strange cats into your original kitty's household? No need to call the "My Cat From Hell" guy?
Cat (n.) A bipolar creature which would as soon gouge your eyes out as it would cuddle.
There have been minor disagreements - light hissing and some retracted claw ultrafast paw smacking from the big boy (Charlie). But no biting or even puffed out tail wild behavior.
We took the slow approach by keeping them in a room for the first few days and letting them out for small increments. Charlie frequently would be outside their door sniffing so he knew something was up. We took the kittens to the vet and left their door open so he could catch their scent, the catbox, the pillows.
The vet basically said go slow to introduce them and if there is conflict let the kittens and Charlie know he is the king of the house and take them to their room. So it took about a week before we let them have a face to face - pretty uneventful, one small hiss from Charlie and it’s when they tried to invade his food. Nope!
Now we leave their door open probably 4 hours a day but close it at night or when we leave. The biggest problem is Charlie eating their food (kitten food has high fat content), and his 21 pounds doesn’t need any help! He’s a biggie. ;p