Movie streams, as in from Netflix, etc...? How do you know they are watching the same thing you are at the same time? It's possible they got your logon and password, but as far as them cloning your video going to the TV to go to their TV, over random wireless signals, that is impossible. That article you read was about tiny changes that they used to detect very tiny data not a streaming movie. We are talking about data many thousands of times smaller than you would see in a video or even simpler things like music. And unless your neighbors happen to be expert computer engineers there is no chance they are doing anything of the sort even to see what you are typing.
If you think they are on your connection you just need to change your WiFi password and your account passwords to whatever services you use. Make sure the account options do not have any strange email or phone numbers added to them.