4 cats intros!

My post history shows the situation we are in

So we adopted Patches (now named Calypso). She is nearly 10 weeks old and has been home nearly 24 hours but Oreo (14 weeks old) is already hissing at the door, hissing at any scent swapping we are doing. Both Oreo and Calypso are eating, tails up, etc., but Oreo doesn't seem happy at all about Calpyso. There are a few reasons why Oreo might have beef:

1- Oreo did have the utility room to herself, but now she is in the living room / kitchen / diner / conservatory (open plan sucks when it comes to cats intros!), while Calypso is in the utility room. ("Calypso stole my room!")

2- Oreo might not know what is in the utility room- it's the 'fear of the unknown'

3- Oreo might know its a kitten but might be unhappy about having someone to play with (she is a VERY playful kitten so this seems unlikely)

We have 2 options going forward:

Option A- Carry on with scent swapping (no visuals) until Oreo seems to calm down, then progress to the next step (site swapping, visuals with one of them in a crate, etc.)

Option B- Show Oreo who Calypso is (Calypso in a crate)

Does anyone have any ideas on the 'best' way forward? We know it is very early stages but we know how important these first few days are! We've also had a lot of stress these past few months and want to make things go as smoothly as possible for everyone involved!