Now two twists that make no sense- the elders are retconed to being above the Celetstial Dragons after already not long ago being established as being puppets of the Celestial Dragons …what? Also, how is Shanks boldly talking casually with them and it not immediately becoming a war but instead an agreed uppn discussion? I wondered if I was wrong and it wasnt Shanks and read posts to try to find out because it honestly made so little sense for that to be Shanks...
About Shanks and the Gorosei I think in OP world aswell as in many series it's possible to talk to your enemy instead of beating the shit out of each other (lol). Talking to each other doesn't mean they are friends or anything or that they are giving up their goals. Kind of a war honor code or something like that.
Also I like to think Shanks being there is quite cool since it could mean even if the WG would want to catch him nobody there could do it or at least the price would be higher than the benefit.
As for the Gorosei they are not above the CD but they are CD, the highest ones. When Sakasuki sayd the Gorosei they were receiving orders from higher above he was begin sarcastic and many (me included) misunderstood it in a different way, but this chapter reveals the true about their status. It makes much more sense to me.
We can't assume the Gorosei are inmortals yet, it's just a non-confirmed theory. I don't see the need for that. Being a CD seems to be something you inherit so there's no problem if they are just mortal regular elders.