u/InterestingQuit7812

So I have two indoor/outdoor cats who have been living this way for two years. Recently our neighbors cat has been coming in our house, at first it was fine because he would just eat some food and sleep. Eventually he started attacking my female cat unprovoked and won't stop. We've talked to the owners who said they will keep him in but they have yet to hold up on that agreement. I live with them part time so it's my grandma who has to deal with this but she is to old be able to look under beds or in most hiding places and she refuses to keep them inside. Any ideas of how I can fix this?