Dear Mr Tanner, Rebecca and Sandra, (If Mr Tanner is the boss it's better to defer to him)
It was very enjoyable speaking with all of you (more personal, unless there were others involved in the conversation that you have not mentioned)yesterday about the administrative assistant and Testing Center Director posts(makes it clear you're referring to both posts) in the Career Training and Development Department at OC Technical College. Both positions sound very challenging and would enable me to use and develop (less pushy- you can be too assertive and you mention it later)my skills and interests.
In addition to my enthusiasm, I will bring to the position strong writing skills, assertiveness, and the ability to work as a team player.
I appreciate the time that everyone has taken to interview me. I am very interested in working for you and look forward to hearing from you regarding these positions.