Third party resources with limeted user rights

We assign task to third party installers. I don't want to give them access to Smart Sheet or view rights to projects, where they have assignments. On the other hand I do want to use the features like sending them reminders or update requests. Most important, I need them part of the Project Resource View. I want to make sure that we don't schedule an installer at the same time on two different jobs. 

If I am correct, you have to add the installers to your User Management on the account level, in order to see them in the Project Resource View. But will that not give them at least view right to see your total project schedule? - Which I don't want them to see. 

Thank you in advance for and comments.