This is a bit of a longshot, but some elements match so I'll let you make your own conclusions. The movie that came to mind when reading your text was "The Haunting", released in 1999, so a little later than your proposed timeframe. It features a haunted portrait that indeed has a ghost in it, and the location is in a large mansion/castle-like building. The movie has a gothic feeling to it, but I can't recall whether or not the portrait changes its facial expression.
https://www.imdb.com/title/tt0171363/
Here's a pic of the haunted portrait as well:
