Yes, to add more facilitators go to 'Edit Mode' of your Siminar. Select 'Add Facilitator' on the right side of the Outline for your Siminar, and you can search for them by name to add them. You will also find option to hide a Facilitator from your course page so that your students see only the the Facilitators you choose. Primary facilitator can also be changed to someone else here.
Note:To add a facilitator he/she would have to be signed up on Siminar.