Danzou didn't seal himself- he only destroyed himself and more precisely the eye of shisui in his possesion. Though chances of him being in the sixth coffin are thin as Madara is in the possesion of his body and he won't hand it over to Kabuto. He already told Kabuto to not puch his luck regarding Shisui's eye.i think danzou sealed himself during the end of sasuke's battle with him.
anko still has the curse mark that oro gave her. it is similar to the one that sauske had previously. i could be wrong here, dont remember all the details.
Oro was sealed by itachi and sealed guys are not supposed to be back by Edo Tensie. But since Oro doesn't seem to be totally at one place only- his chakra stored at several places and being able to take over the body ( eg in case of Kabuto) it's different than Minato's chaka left in Naruto which depleted with use. that's why I was wondering about his soul and related concept as well...