Compromise on the questions first
The purpose of HR staff sitting in the interview board is sometimes to try to make the interview more "objective" since there is a third-party involved. And they are 'supposed' to be the experties in interviewing and understanding what questions are valuable and effective to find a suitable candidate (oh! but sorry, I still can't meet such HR guys so far in my over ten years working life.)
Anyway, to cope with this, I'd suggest you to list down all the basic questions and communicate clearly with your HR staff beforehand to get a mutual understanding on the objective of each question. I think it's not a bad idea as, to be objective, we should ask some sort of "standard questions" to all the candidates and then the supplementary ones according to the candidate's response. Only we've a "standard" as a ground and get the comparable results can we evaluate objectively the candidates performance. I don't think it's a fair and effective interview by asking arbitrary questions (even ifrelated and sensible) to different candidates and then choosing the "right" one just based on the perception on their responses.
