My cats just started fighting! What should I do?

I have three cats and a dog.. One cat, fudge, we've had for about 9 or 10 years, he's a male but not part of the problem... Our female cat, tasha, we've had for 6 or 7 years and the last, Casey, is a male who we've had for 2 or 3 years. So on Thursday at about 5 in the morning I woke up and heard 2 of our cats just screaming and fighting- tasha and Casey. Now they can't even be in Tue same room together without starting a fight. They havent major hurt eachother but tasha has a scratch on the nose and Casey acted as maybe his back side was hurting, but then again he's a touchy cat, he's really a brat.. lol.. and tasha is this big overweight calico who is very tense and jumpy at all times.. we bought some anxiety drops to give them and it made them all happy and tasha much more relaxed around us but as soon as they saw eachother again, they growl, hiss, and try to attack eachother. We have too keep them locked in separate rooms or have one in a pet carrier now. I have no idea what to do because my mom is really mad and says if they don't stop fighting we will have to get rid of one or both of them.. Please Help!!