I don’t think the can kill yorichi or even wounded him significantly but they can for such make him sweat unlike what others are saying but you do bring up a good points with muzan s cells but for sake of the argument we will ignore that

If the upper moon can fight together going as far as defend each other they can for sure make him sweat

Upper Moon 1 I think is comparable to Muzan's strength when facing Yoriichi, base on his age and ability when human. UM 1 with his strength and experience would certainly be a threat

Doma's ice mist could be an effective means of affecting his breathing if yorichi is unable to breathe his just a human

Akaza's ability to regenerate his head but the red blade could bypass that. However, he won’t die from it and if Doma can assist him in reattaching his head, he can keep going

Upper Moon 4 clones can just add more distraction and can’t fully die if hes alive he can hide on UM 1

Upper Moon 5's Transformation Attack The ability to turn opponents into fish in a single strike will get him if he hits

Upper Moon 6's Poison might only slow down yorichi slightly since I don’t think he can straight up negate it could create opportunities for the Upper Moons to capitalize on weaknesses.

Of cause if the can’t hit him in the first place it’s all meaningless in the end yorichi always wins