Highly unlikely you can retain your tenants while selling the house.
Firstly, no matter how nice your tenants are, the house is not going to look as well with people living in it and all that entails versus having it empty and staged.
Secondly, your tenants will need to agree to certain access times etc which may end up being inconvenient for them or the agent.
Thirdly, if you were a tenant, the first thing you would do if the house you are living in was being put up for sale would be to look around for another house. And as soon as one becomes available they will take it - because they need certainty of tenure
So.. the best option is to have the house empty, touched up and ready for sale. If you can't afford vacancy to enable that, I think you would be best to delay the decision to sell until such time as you can afford to do so..