I feel like an idiot but I have no idea what to do on "Restless" and the description doesn't tell me anything. It makes me think I have to rest all Nesses, but I tried that and no cigar, I used sing on all of them, I tried KO'ing all of them but haven't managed to do it yet cause the time limit is so friggin short... someone help me out here please?

You just use sing.

Maybe it's bugged. I hit all 3 with it and did nothing.

at the same time?

the event's title it's "RESTless" and the image shows Jiggs using REST instead of the move you need to use "SING" which may confuse newbies.
Honestly I find it as a hilarious red herring so I say keep it

I know what to do in the event, but I often just wind up using Rest on the little brats anyway out of sheer frustration because of all the ledge camping they do. Not only does that make them invulnerable to Sing (because it only works on grounded opponents), but it also makes a lot of repetitive noise.

YOU WANT SOME REST? HAVE SOME REST.

I find this event a bit too RNG dependent. It's rediculous to try to get them all asleep if they get to opposite sides, so you need to get lucky and either dash attack them all at the start, or just sing and hope they all run into you. I've completed it both ways, but otherwise... good luck.

You have to start the match w/ the nesses in a line in front of you

Dash attack
Sing
Win

Lol you just need to dash into the middle and sing.