Lots of silly replies to this, going to try to offer some real advice here.
First off, I didn’t believe in ghosts either until I experienced one. I believe that your tenants are seeing what they chose to see and that something real may be going on, But you didn’t ask for our opinion on that.
From a business perspective you can simply give them their options, the way I see it they have 3:
1. Do nothing and continue living the way they are, 99% of ghosts are non-malicient and will do them no harm
2. Continue living there and take steps to get rid of the ghosts as long as those steps do not involve damaging or altering the property in any way
3. Move out and pay the penalty of cutting their lease off early, maybe offer them their deposit back if they leave the place spotless and also help you find the next tenant?
In the meantime if you are in a ghost-centric town you could potienlly monetize your haunted house! Hope this helps!