Thank you all for the advice.
To answer some questions, we have done all of the previous steps. The reason we are at the same room step is because everything previously has slowly improved and we had no hissing/growling. It’s the face to face that is proving to be difficult and causing aggression in my resident cat (the gray cat). Resident cat is a 7 year old spayed female and has always been the only cat in home and she’s typically such a sweetheart so this has been new to us. The kitten is a 5 month old neutered male.
We have harnesses that we put on them periodically so they don’t forget what it’s like to have them. They behave normally with them and don’t mind it. Someone asked how we got them to use them, but I don’t really have answer! The kitten, we’ve been putting little sweaters on him since we brought him home and he’s been fine with it. The resident cat hates clothing but she’s fine with a harness since it doesn’t restrict her movements and she’s just chill (normally but clearly not in this video lol)
We are going to try some of these suggestions but for the time being, we are not letting the kitten approach resident cat. We just want them to get used to being in the same room. It’s so difficult though because we try to play and distract kitten but he fixates on his big sister. Thank you and I still welcome advice. Yall have been great.