I have personally found that I need to try and avoid the cues to coax the sacrum into nutation. I have experienced pain when the sacroiliac joints get out of place!
About the name of the sacrum, I read somewhere that it was thought that this bone was not subject to decay! Perhaps it survived longer, intact, than other parts of the skeleton because of its density...

I haven't hear that before Kate interesting!

I heard that if we didn’t keep both sitting bones on the ground in a twist, this could cause a kink in the spine. I’m assuming they meant lateral flexion. Any thoughts on this would be really helpful

Bryony F my guess is that they mean one sitting bone is not higher than the other (ie one off the floor) this sets the spine up for a possible kinky twist-heheh- but i'm all for sliding one back (rotating pelvis) is a seated twist rather than trying to keep them absolutely square which if the twist is aggressive could create instability in the SI or add stress to the lumbar vert- does this make sense?