It doesn´t matter if they know how to sing or not, is not like they will sing live, they may record the songs 1st and then just move their lips on filming, especially since there will be dance numbers and with all modern technologies even the worst singer in the world, has a voice that can grants them a grammy, from my knowledge only Colin can sing for real, all the others can suck but then on the episode, with the effects will show that they all have great voices.
Also the asterisks, what do they mean? are those the scenes that won`t have any singing? or are the scenes that will have singing?
Are you implying that some cast members could end up being auto-tuned? Guess that possibility can’t be ruled out. And yeah, apparently the asteriks do mean those scenes will involve singing. I heard Paul had an Instagram video, which may be where the initial photo originated from, and “*Denotes singing [third word cut off]” was visible at the bottom of the page.