Selling property with tenants that wont leave

G’day,
My wife and I recently separated and have decided to sell one of our investment properties for financial reasons alone. We received a very good offer subject to vacant possession, however the tenants are reluctant to go despite offering a few thousand dollars cash for the inconvenience and a real estate offering to help them search for a new rental. As this was a financial decision, we are now considering giving them notice that we intend to raise the rent in order to cover our financial situation of being seperated and having more costs to incur. The property is currently rented at least $20-40 a week below similar properties in the area, however we feel that the tenants will try and contest any increase. I dont want it to look like we are pushing them in to a corner, however the best case scenario would be for the sale to go through. Does anyone see any problems with the steps we would like to take which would result in either a sale or increased rent? Any help would be appreciated. Cheers
tugger