I would send the thank you letter to the person you've been in contact with for 3 days and mention the other interviewers name in the letter to that person. They introduced themselves that way, that's all you have to go on, unless you look it up. If you look it up, it might show you have more interest in the position than they might had thought you did.
Simple, people are subject to errors. Call back to the interviewer you know, simplly ask, what is the other person names. Be happy about it, and say their name slip your mind. Next time take notes, always call the person name out so you can here it. Helpful, this is what I do. BEST WISHES, Hope you get the position!
If they have a website, look up the names or just put, "to everyone involved in the interviewing process" or something to that effect...
Call and ask the secretary for their names.
Ooh. That's a tough one. You may not be able to personalize it then--like "Dear Hiring Committee"
Call the Gatekeeper. Probe her/him for the information. Being upfront and candid that you just interviewed, they'll tell you more than you can imagine ...
Consult with their receptionist or secretary. Say that you had an interview and are inquiring about the correct spelling of their names.
Hmmm. Pizza and "special brownies" might just do the trick. You could get hired on the spot.....unless it's a CIA job.