Costello is fighting with a ghost in the dark and shouts that he's going to take off its sheets and see who it is... the lights go on, and the woman who was also there is whacking him with the 'how dare you' look.

A corpse is shown with a little blood at its mouth. This is more "frightening" than "violence/gore" especially by modern standards.

Absolutely none at all.

People drink / drinks shown. Only in a very social way, and mostly ignored for dramatic situations.

The second half of the film can be a little intense: it's a "haunted house" film after all - but with the comedic tone added by potentially the most famous (and rich) comedians that ever walked the earth.