I like 4plexowners’ ideas. But, as a landlord, I can tell you that they likely already understand that a $200 drop in rent is better than 2 more months of vacancy in terms of annual gross. If they do not understand this, then they will not likely agree to your offer anyway, because they are either bad at math or weigh other factors more heavily than optimizing income.
Believe it or not, there are sometimes valid temporary reasons for holding out for higher monthly rent and accepting a bit more vacancy taking less annually.