my side lights make my passenger rear ( and only rear) indicator come on any body had this before i changed the lights because i thought it was that but clearly not
and it also makes my drivers rear side light flash like an indicator

An iffy earth connection it's as simples as that.

I was sitting behind a car yesterday at traffic lights and the right hand brake light along with the high level brake light were flashing in time with the right hand indicator or though the rear indicator lamp was not flashing all I could see was the side repeater, I did wondered how long that would remain undetected, maybe for a long while as the car had a young femail driver.