I saw this happen up close once. A couple applied for a senior position, asking to be considered for a shared position. Throughout the interview process, they kept arguing that we would be getting two for the price of one, etc. Then we made them an offer, at which point they switched tack and insisted on two salaries, two research budgets, etc. The dean was so pissed we nearly lost the hire altogether. They eventually worked it out, but there was a lot of ill will, and I doubt the university would have been amenable to hiring others for "shared" positions for a good while after that, if ever.
You still wanted to hire them after that?