Kitten and older cat help

[NauseousNancy]

I have two 8/9 week old kittens and a 4 year old cat.

We got the kittens at the weekend. They are in their own room, with food & litter etc

older cat seen them through the window and hissed. She then came in and was sniffing and pawing at the door so opened for a sniff. She won’t go in, but sits at the door and hisses if she sees one of the kittens. She growls and hisses but doesn’t run away, and no puffy tail or arched back.

I can’t keep them in there indefinitely, what steps do I take next? They are desperate to explore.

i brought a blanket the kittens had been sleeping on out to her to sniff but she hissed at that as well.

help please!

Can anyone help?

We moved to opening the door and putting wire across it so they could see but not get to each other for a few days even we were present, then supervised meetings for short periods. Also fussing the old cat, and moving their food close to each other. Not sure it made much difference though as a year and a half later they still fight.