I am of the opinion that Cassiel should have a diplomatic bonus towards Einion Logos. Cassiel probably knew Immanuel Logos personally, and would have greatly respected him for abandoning the priesthood of Sirona in order to care for the orphans of the godswar with no regard for their religious beliefs. Immanuel may be a personal hero of his, as well as an old friend and even a big part of the reason he decide to abandon Dagda. Einion Logos is doing all he can to uphold the legacy of his predecessor, and is also noteworthy for defending against the Infernals without going out f his way to wage a crusade, and for opposing the increase in hostilities caused by unleashing the Mercurians. Einion and Cassiel seem to be kindred spirits, and I cannot think of anyone Cassiel would respect more. (Now that I think of it, Cassiel may very well have been the one who decided that the Elohim should be present at the Seven Pines for the signing of the Compact. Even though he could not bring himself to agree to the final terms, it was Cassiel who convinced Dagda to call for it. For all we know, it might even have been Immanuel's idea originally. Anyway, if the Elohim had not shown up there then Sucellus would not have tasked them with caring for his holy sites, and they would be nothing like they are today. Cassiel and the Elohim have close ties dating back long before Kylorin was even born.)
Ethne the White on the other hand, abandoned just about everything Cassiel admired about the Elohim. She was also originally chosen to be queen because of her practicality, a trait Cassiel doesn't really care for. I'm not sure if this is really worth a penalty, but he should at least have no bonus towards her.
Cassiel and Sabathiel are also known to have been good friends, and to respect each other even though Cassiel really doesn't like that Sabathiel still serves Junil and Sabathiel does not like that Cassiel abandoned his duty as archangel of force. I think a small bonus between them could be good, but nothing too big least it let the Bannor drag the Grigori into a crusade.
Although Sabathiel and Basium are both archangels leading militant, anti-demon civs, the scenarios seem to indicate that they don't get along. Capria specifically states "But beware for faithful Sabathiel told of stories of Basium, and he is unbound by mortal virtues." Sabathiel's character is defined most by Loyalty (I'd almost say hesed, but it may be best to save that as a term for only the perfect love characteristic of The One), and Basium has proven disloyal in the past. He abandoned his god, and didn't have nearly as respectable a reason as Cassiel did. Perhaps even worse, he has a deep hatred and jealousy for the current god of life, who should rightfully be his master now. He is not content to play the part set out for him, and is covetous of godhood. He constantly flaunts the rules in order to pursue what he considers a higher good. I'm not sure if Basium should have a penalty towards Sabathiel or if Capria should have a penalty towards Basium, but I don't think Sabathiel should like Basium very much.
Obviously, Basium, Hyborem, and Cassiel should all really dislike each other.
Kael has stated that Basium almost destroyed the Sidar, who survived only with help from his sister Gyra. I'm not sure if he really had something against them personally or if he just didn't like how they refused to join his crusade (although Kael seemed to imply the latter). As such, I'm not sure if Basium should have a malus towards Sandalphon. I'm also not quite sure when this happened. The scenarios do however state that the reason Sandalphon sent Rathaus to kill Ethne and trap her soul in the underworld was because she was going to release Basium. It may be that Basium had come earlier and almost wiped the Sidar out, and that Gyra was able to hold him back until the Mercurian Gate was built. In that case, the Sidar likely hold a huge grudge against Basium even if he is indifferent to the Sidar. They may have a grudge against Ethne too.
Perhaps a bonus between Ethne and Basium would be good, and a malus between Einion and Basium.
Ethne and Dain seem to get along well, and should perhaps have a small bonus between them. Valledia is described much less refined and has never particularly cared for the Elohim, so she could possibly have a tiny malus towards their leaders. Her crudeness however is described as being a boon in relations with the dwarves (she is a lot of fun during drinking games), so maybe she should have a small bonus towards them. If Einion ever figured out that Veledia was behind what happened to his wife, he would likely have a big malus towards Valedia (although he is likely the type that would forgive even her, at least if he thought she had/would change).
Although they both now work for the destruction of the world, I don't think Tebryn would like Hyborem very much. It is Hyborem who claimed his soul and took him to hell, which as we all know he really did not like, and who would likely take him back there if he displeases his new goddess. Perhaps Tebryn should have at least a small malus towards Hyborem.
I'm thinking Varn should have a major grudge against Lethe for taking his wife from him. I'm thinking at least -12. He hardly cares about the other demon lords, but he really wants her to pay.
I'm thinking Falamar should have a malus towards Perpentach while Perpentach has a slight bonus towards Falamar. This is basically just like the relation between Beeri and Perp, but shouldn't be as large since he wasn't there as long. Such a malus/bonus may be appropriate between Perp and all the contestants in The Momus.