Thank you note to two interviewers on same interview without email address

Just had an interview with two interviewers and wanted to send thank you notes to both of them. Their email addresses were not provided, and their names are pretty mundane so there are several people within the same firm who have the same names. 

I wanted to send a thank you note to HR and ask her to pass on my gratitude to the two interviewers by adding some words on the bottom of the email sent to HR (if this would be a good idea). Wondering if I should write two separate notes or just one note addressing both interviewers in this case. If two separate notes, they would be essentially the same though given that one interviewer actually barely said anything during the process.

Appreciate any help.