Introducing cats- HELP!

Hi guys, I literally just signed up for this forum so i could get some help.

I am trying to bring another cat into my household, but I've run into a common problem, one doesn't like the other

Original- girl, New- boy

I tried separating them , but my original cat is so excited about this new cat that she won't stop hovering around the door and keeps putting her paws underneath. And when I say excited, I mean it literally. Where the new cat is hissing and growling, mine is just meowing and acting very calm. If I got her a kitten to play with, I swear, she would be ecstatic. She is definitely not one to pick fights.

The new cat on the other hand is the more aggressive one. My boyfriend, the original owner, said that he gets really stressed out when he is put into a new place and that it takes him a couple days to calm down. But that was only when he was with his sister, not other cats.

When I had him in a separate room, he would hide all the time, hiss and growl a lot, and swat every pillow or blanket that smelled like the other cat.

I was able to get him to play a bit, but he would even growl while he was playing or rubbing against my leg. I really don't understand him, and my bf is just as confused as me because we have never introduced him to other cats on his own.

Do you think Fellaway would help at all, or would it just help with him locked in the room and not work if I were to let him out?

Should I remove everything that smells like my original cat from my room until he calms down too?

Thanks in advance.. 

Also, these are not young cats

The original is 14 and the new cat is 6 or 7

They are both older cats, they need to be isolated until they can deal with each other's scent. A lot of the time aggression masks fear or at least great discomfort . The thing is to get the new cat to feel safe and confident in it's new space.

The growling while rubbing your leg is called re- directed aggression, the cat is wound up tight and feels like it has no outlet for all the frustration.

Feliway may help but they need to be separated until the new one no longer responds negatively to the smell of the other cat.

Don't remove the other cat's smell, you will be going backwards. It's going to take some patience to 

Playing with the new cat with a fishing toy will help discharge the pent up aggression. If he refuses just sit down near him and talk to him or read to him. The idea being to reassure him. 

Here are some articles which can walk you through the process but I can't emphasise enough that you are going to have to take things very slowly. 

Article] Re-directed  Aggression  in Cats

[Article] How To Successfully Introduce Cats: The Ultimate Guide

[Article] Introducing  Cats  to Cats.