cats hissing at each other

i have 2 cats, brother and sister, my mom who lives next door also has 2 cats, mother and another sister. both sisters were fixed few month ago while mother and brother were not, today i fixed mother and brother and when i brought the mother to my moms place, both of her daughters started to hiss and growl at her!
they dont have this reaction to the brother. the mother was still walking funny, may b thats what triggered this kind of reaction. before the visiti to the vet everything was fine.
i brought my cats home while other 2 that are at my moms place had to be separated in different rooms
im really concerned as to why this happend and how to fix this

The mother must have picked up the strange scent of meds and of different animals at the vet. Also if she's still recuperating from surgery, the other cats sense her "helplessness" which can also trigger the unfriendly reaction.
Separate the mother until she's fully recovered and start reintroducing her to her daughters. The stickies have great advise on cat intros.

I agree. It's very common for cats that come home from vets to be hissed at by their companion cats for the reasons that Yayi talked about. Separate them and give mom time to heal.

Good job fixing the kids btw!

Vet/surgery smells trigger various reactions. After they heal, things should be better. Anytime I bought one of the pets home for the vet, the others would growl/hiss at them for a day or two.

thank you for your responses. isolation did help, today there is no more hissing or growling, daughter is just staying alert and not coming close, otherwise things are back to normal.