What would you do?

wow, it's tricky, really tricky.

in a normal situation you would just respect their saved spots. however, you may just moved them because they didn't respect a hotel's rule and it's unfair. the problem would be if they arrived and set up a fight with you, which would be totally embarrasing for you both.

I would just go to one to the hotel's personell and talk to them about the situation, so when they arrived angry, you call one of the crew members and he may explain them the rule. maybe they won't fight about it because they were covertly scolded.

that's what i would do

At check in discuss this with the desk person to save yourself the aggravation. They might tell you what you want to hear. Hotel employees are usually not permitted to remove or touch guests personal items unless they've checked out and they go to the lost and found. Find out the rules. You may very well be able to move the chair and then you know the rules in case of confrontation by the chair owner. That is rude of them.

Well, I'm a Mexican, so I would say, the hell with it and go early to reserve your spot. but etiquette would be to report if no one shows up on time. By the way, have fun in Maui, rather be there than in school.

I would ask a hotel employee to remove it if no one appears after a reasonable period of time.

BTW - Have fun. Wish I were going