A few Lore clarifications and questions for Fortunes Weave

Hello! It's been a while since I've played through Three Houses, and while i'm playing through it now, I don't know if i'll be able to finish all the routes in time for FW, so I had a few Lore clarifications questions, and theories I wanted to run by the community. To start, here's my current understanding of the relevant lore for my thoughts.

1. From my understanding, Crests and hero's relics only came to be after Nemesis and co killed the naebatans and got their blood and turned their bodies into the relics. This started with Sothis herself as the first one. The majority of crests came about this way that is, I know the apostles got theirs from the naebatans willingly for instance.

2. The naebateans were only in fodlan, and after the purge from nemesis and co, only 5 remained( Rhea and the four saints).

Based on those points, here are my questions:

1. If crests are a thing in dagda, how is that possible without a retcon to the lore?

2. If the gods we see in FW are naebatans, why did they not go and help rhea/serios to get revenge on nemesis and co? it feels weird to me that a big part of rhea's character is her survivors guilt(hence her covering up the truth of crests and stuff) just for them to go "oh btw there's more over here in dagda that just chose not to do anything".

And now my theories:

1. I think the "Adult sothis" we see is in some form sothis in Byleth's body. Sothis is revealed in her s rank that her existence is tied to byleth's soul directly, including in crimson flower. In addition, it's revealed in three hopes that sothis is able to just..... take over byleths body at will. Because of this, I am running under the idea that sothis took the body and...... somehow took out byleth's "half" of the soul and turned them into Eshmael, potentially wiping memory(to explain the "have you forgotten me already line" she has in the trailer).

2. I think the dagdan gods are another dragon species potentially also from the Blue Sea Star, that are able to give abilities that do the same thing as crests, but are not the same thing as the fodlan crests, but happen to have the same symbol. this could explain why Esmerelda having the blaythd crest is possible, as well as how we can have returning crests without breaking the exsisting naebatean lore(to my current understanding of it at least).

I have more smaller theories(like my idea that ninae is flayn), but these are the biggest ones that I have massive questions about. I'm almost certainly missing things because of how long it's been, so any discussion is appreciated! I'm excited for the game to release.