Help,  I saw this movie on video in the early nineties.  It was probably made in the late 70s-80s.  It’s in color.  It’s about a brother and sister ghost who haunt a mansion estate in I think England.  Whenever they disappear from the present they actually travel back into the past where they are still alive.  They befriend a boy in the present who by the ends helps them change the past so they and their best friend don’t die.

I remember a scene where the stepmother of the boy and girl left the windows in their room open to hopefully kill them through exposure.  Their best friend (a boy) climbed up through the window and stuffed newspapers in their blankets to keep them warm.  Later the stepmother was upset saying they should have at least caught a cold or something.  The best friend was supposed to have died from falling out of the window,  but that changed too.

I know it’s complicated,  but it was a kids movie.

The past (flashback) scenes look like they take place in the early 1900s.

There’s also someone who talks with the present day boy about the kids,  but I don’t remember much past that.