It depends on the tenants motivation. I find it is always a good idea to set expectations up front and if you feel the tenants may have an issue when the time comes to sell don't rent to them. Since you have tenants in place you may want to assure them that you will respect their privacy and work together on showing times etc. The outcome of a situation can depend greatly on how it is presented...
Linda, if you have an account, go to this link: http://www.trulia.com/submit_listings/
You can post a listing if you're not an agent. Click on submit a listing. You will want to change the drop down to either home seller or home owner.
If you need any assistance, please email me and I will assist. I still work the cape often and if you need professional assistance to get your property sold at a premium, I would be happy to meet with you.