If you think this is home invasion, how about picking up a gun and start shooting? Home is your castle, right?
No, this is not home invasion. A similar and more common situation is that in many foreclosed homes, the previous owner have possession of the house but lost ownership to a bank or whoever won the auction. When the previous owner refuses to move out, the new owner cannot charge in, he cannot start moving furniture on his own, he cannot change the locks. The new owner have to go to court and file for eviction.