Sorry to hear you're having troubles with your furbabies getting along. When you say mean can you give some examples?? I guess what I'm asking is are you sure it's just not normal dog behavior?? My 20 lb. bichon/poodle mix plays rough with my tiny shih tzu sometimes but she loves it and keeps going back for more!! Sometimes I shout at them to stop and and they stop and look at me like I'm a lunatic then go right back to wrasslin! Give some examples of the behaviors you're seeing maybe people can comment more specifically. Good Luck!!!