How to re introduce cats?

[Kris]

So about a year ago my sister was living with me, she has a male cat. I have 2 females. My sister and her cat lived at my house for 4 years before moving last year. About 2 years ago I took in the girls and they got along great. Her male (name is Tripod, since he only had 3 legs) basically loved them. I would find them all cuddled in a pile in the basket, he would clean them, and everything was fine. So last year my sister moved and took Tripod, but now she came back yesterday and the girls are a total disaster now. They are hissing at everything that moves including each other. Half an hour before Tripod came in they were sitting together grooming each other and happy, now they won't even go near each other and hiss at everything. Tripod isn't showing any aggression, he is a bit on the older side and just wants to sleep on the bed. So is this something that will just take time for them to get use to again? Is there anything I can do to help them readjust? Also, both girls are spayed, the male is not but the vet doesn't want to put him under anesthesia any more then needed because he has quite a few health problems. Would him not being neutered effect them adjusting to him?