Thank you Letter after interview?

I had a job interview for a position and interviewed separately with four different people within that department, one of them being the Vice President for the department. Now, I have all the emails (through the HR), but I am unsure who to send a thank you email to.

If I send each interviewer, than I will need to change each letter. I was thinking of just sending one to the VP, because the others work under her on the same team (except one). Would this be appropriate?

I made sure to thank each interviewer after my interview in person.

What do you think is the best approach?

Thanks