Adding new kittens with a 4 yr old cat

I have two 9 week old kittens, both males that have been living in a bedroom since they were just over a week old with their feral mother. She is going back outside but I need to figure out a way to introduce them slowly to my 4 yr old female who hasn't lived with other cats before. She knows they are there because I have shown them to her twice and she is always at their door when I come and go. I would love to put up a pet gate or baby gate so everyone can see/smell everyone else without any fur flying for awhile. Unfortunately after a bit of research, I can't find anything tall enough that the kittens couldn't climb.  Does anyone have any other ideas? I will definitely give them supervised time together anyway but I thought if they can see each other 24/7, this may make things easier. 

Any tips would be appreciated. 

You can put in a screen door.

I am in the same boat! My older cat got aggressive with the new kitten, need some help!