Technically you have to tell the car rental company if somebody else is going to be driving. What then happens depends on the company, though at least several rental companies will allow your spouse to also drive the car for no extra fee. Two people handing off every few hours can fairly easily do 24 hours straight safely (provided both are semi-decent at napping in the car). With three people or more, as you said, it becomes trivial.
Even in cases where the rental company charges you for additional drivers, I don't think that charge ever goes over a handful of dollars; not really enough to offset a 24-hour straight run.
From what I can tell, rental companies dislike multiple drivers because multiple drivers increases the risk of incident (I presume because multiple drivers correlates with 24-hour runs).
Even in cases where the rental company charges you for additional drivers, I don't think that charge ever goes over a handful of dollars; not really enough to offset a 24-hour straight run.
From what I can tell, rental companies dislike multiple drivers because multiple drivers increases the risk of incident (I presume because multiple drivers correlates with 24-hour runs).