My cats hate each other after old one dies...?

I used to have a cat named Jaxson, she was at least 14 when we got two new kittens. She avoided them very well, letting them know to keep their distance in a very nice way. The two female kittens loved each other, even though they were from different litters, they were the same age, 3 months and they loved each other as soon as they met each other.
The older cat had something like a stroke maybe a year after we got the kittens. They had been getting along great until we had to put Jaxson down.
Now, they simply hate each other. They cannot be in the same room together and either will hiss as soon as they see each other.
It hasn't gotten really physical, thank god, but its really sad to see them hate each other so much.
Do you know of anything I can try to make them love each other again? Or like maybe minimize the hatred so that it doesn't become physical fighting?

Perhaps like dogs they have a pecking order? So now they have to decide who is top Dog as it were. Being the same age makes it a bit harder.

it won't really become physical. they are just trying to see who will be next to be dominant cat. so you as a owner to chose who needs to be dominant. the way you do that is by giving one little more attention. i now it sounds men but i know what i am talking about.

sadie u dont know wat u r talk'n bout, those two cats will figure it out them selves, if u give one cat more attetion u will most likely make it worse u dummy.