Animal Welfare Professionals

I recently adopted a 7 year old pit mix named Thumper to be my new support animal after my Sandy passed away. Between me and my Mom we have 3 cats total that live in the house. Thimper has no problem with the cats and ignores them the best he can. He is scared of them and that lines up with what the shelter told me. Two of the cats, who are nearly a year old pair of brothers, actively stalk and attack him. Not just make the noises and hiss and screech but seek him out and attack him. I'm afraid for their safety. I've tried putting him in a room while I'm gone only to come home to property damage. I dont want to have to decide between these animals that I love with all my heart maybe more than my family. I need some strategies to try!  I feel that if they stopped viewing Thumper as a threat everyone could all just get along. And if he could roam the house free of their attacks it would eliminate the damage to doors and carpeting. I am desperate! Thanks in advance!

A lot of people accidentally cause some issues when they introduce pets to a new pet by just putting them together and hoping they'll work it out; that often isn't the case. I recommend going back to square one by splitting them up and only doing supervised interactions (maybe starting through a baby gate) where both parties are occupied. A good example would be feeding everyone at the same time on opposite sides of a room or opposite sides of a baby gate. Another would be feline playtime in a room while Thumper sits quietly (maybe while being fed treats to distract him) on opposite sides of the room or in the hall outside the room (and maybe through a babygate). 

Many of the following resources focus on dog-wanting-to-chase-cat, but the methods are still applicable for the reverse. 

https://resources.bestfriends.org/article/how-introduce-dog-cat 

https://www.animalhumanesociety.org/behavior/how-introduce-dog-and-cat

https://www.americanhumane.org/fact-sheet/introducing-dogs-to-cats/

I would also recommend crate training with Thumper for when you're out of the house (to avoid dealing with destruction). I would shut door to the room the crate is in the cats can't harass him in the crate and turn the crate into something scary. https://www.humanesociety.org/resources/crate-training-101

I also want to say - meant as kindly as possible  - you shouldn't expect a miracle overnight. It took about 6 months before I trusted my dog to be un-crated in our home without supervision... at which time he upgraded to being loose in one room. It took an additional 3 months for him to have free reign with the cats unsupervised. That's a lot of time and effort, and it is okay if that is more than you bargained for or are able to commit to at this time! I hope this helps!