Wouldn't this be both good for the polite form of "Would you wait for me" or the plural form "Would they wait for me". I don't see where you could distinguish one from the other, but the lesson marks you wrong for "Would they". This is the same problem throughout this Duolingo German Course.
I also use wait on sometimes as a native American English speaker in New York City with the meaning of wait for. However, the way I use it is a bit nuanced with a negative tone. If I felt that the thing being waited for was a nuisance for whatever reason, I would be waiting on it.
You're meeting your friends at the packed movie theater, it's cold outside, and you're running a bit late. You guys don't have to wait for me. (I'm going to be a while so don't wait until I get there to start watching the movie.)
You're working on a project with some classmates. You have taken an extended amount of time to complete your part, and everyone else is done with theirs. Today, you finally finished your part! You guys don't have to wait on me any longer! (You will no longer be a nuisance/hindrance to the completion of the project.)