How can i protect my cat from being beaten up?

I have two cats at home, one short haired the other long, they are brother and sister and are fairly small farm cats. A family recently moved in down our road and they have two Bengal cats which are known for being exceptionally vicious (our vet said they have to anesthetize them before doing a routine check up). One of them repeatedly comes over to our house and attacks both of our cats which is costing us a fortune in vet bills, they have been outdoor cats for their entire lives so we are reluctant to keep them indoors in case they get out and run away due to the change. Is there any way to prevent the other cat from coming over and attacking ours? Thanks x