2.
Ella seems to be chosen by Memory but she was infected by Body. Both have active communication with her, but with the latest knowledge we got from the update, we don't exactly have a role for Body to fill. During deadend3, Ella calls Memory. The 50-50 hybrids seem to be Memory's project with Body being along for the ride.
Ella could have a 50-50 compatibility but failed to awaken memory trait (or only partialy), and once Ella was judged as a failure (after she failed to kill Christie), the 4th still used Ella to find another suited candidate for her experiment.
It would also made sens with what Sylla said about her being used for something else by the 4th. and also the signification behind "suitable to birth", Since Ella found mc and does everything in her power to ensure his growth, and also tried to create other like Jake or Michael.
But Ella is both 3rd and 4th chosen , during dead end 37 mc in is arbiter form refer to her as "their chosen" , and we see just after that he talk about Ella
and that lead me to think , coupled with how the chosen are presented to us and what we can see about apostle and arbiter (6Arbiters, 12 Apostles,6Chosen) that they arent more than 6 chosen, only one per pair. and that each Chosen heart is needed to reborn the 6 arbiters.
no mater what, Aglaecwiff will conceive a child, either with Deryl or Mc and from what we know of the creature she inspired with, he will be an ennemy, even Valravn warned us, Also Aglaecwiff want a child "strong and powerfull.One so great he could challenge the gods themselves.."
Valravn also talked to mc about a futur fight between the two of them, and his heart was convoited by Ella, but was given back to him by deus (likely to ensure mc growth so that he's ready for later, and he also the one killing mc if he fail during dead end 37)
That chosen with red Lightning and a sword have great chance to be an ennemy since his connection with mc and him be locked by Sylla in mc memory.
The fairy isnt an ennemy per see, but the 6th wanted Alice to devour him, and with him be shown as indecisive, he could let alice devour him and his heart. Alice is a determined and strong willed women who could do what he couldnt, oppose to monster kind way.
Rebis guide Tanos through is research with twins so he could offer them his heart when they will be ready of he could become hostile and be killed by them .
Eiseth is captive for now but definitely a threat and during her fight she can have some control over reality despite beeing a chosent of truth, it lead me to think that Reality could be the 4th arbiter like Order,Evolution and Infinity.
A possible futur war between them could happen since Valravn refere the 2nd as ennemies and Valravn also attack mc if he think that we'r allies with the Fairy , also, later in his cellule when he know about mc lineage and talk with him, seem convinced that the two of them will fight.
We could have a conflict between two side with 3 Arbiters chosen, and with that we could maybe made a link with the Outher twin, two combination of 3 arbiter power Order Evolution and infinity against the 3 others. ( but of course it's purely a theory for this last part ^^)