Well when I 1st heard of Osiris I found them to be 3 possible things - illuminati like, Riddlers, & a Lost civilization or group. Which was a lot like you said in Part 1 however I did not catch the egytian reference till you pointed it out, don't forget Egypt also had connections to The Roman Empire also we know Egypt's pyramids relate a lot to space. Now you I don't know if you noticed but look at The Eye the center looks like a star or sun which can mean a lot of things. In our real world the closest thing to physical Gods is Planets & The Suns in our universe. Which also translates as life as The Sun affects a lot of life. Their is also a Sun God in egyptian culture if I recall correctly. Seraphim are basically Angels &/or Angelic Guardians so your research was correct their, however too little is known to be sure those 2 are enemies, they may just be rivals but not enemies for all we know. I wondered if Osiris found something that collapsed them. But I digress, I assumed 7 Seraph's, going by they're name, are a Eliteist group that come in on extreme situations, best of the best or something of the like, we know Arch Angels are known to bring great power to a battle-feild. We'll see more at release, however I would not be shocked if Osiris was always mysterious, you may have to do something special to join Osiris or 7 Seraph's.