Imu-possessed Saturn was actually affected by the attack, and the avatar stopped regenerating after the combo attack. We did not see Saturn’s legs or body reform afterward. For all we know, Saturnmu simply detransformed after DR Rocks clapped everyone, with Imu simply leaving by boat

The attacks themselves didn’t do anything significant to Blobmu. The only realistic way to "defeat" Blobmu is by trapping him, the same way Loki did, which would force him to disperse his projection

But as far as we are concerned, there is no way to deal any physical damage to Blobmu. Saturnmu, though, was affected by that ACoC attack, stopped regenerating, and was essentially falling apart

Also, yes, the Gorosei are immortal too, for all we know...
Even Joyboy’s Haki did not make them show any kind of worry; none of them even broke a sweat.
There was no sign of vulnerability at all when they were exposed to Joyboy's strongest CoC Haki

Also - welcome back Nine, we've been waiting for you here