Those are fabulous. I’ll add an old and terrible meta-theory and expand on it to apply it to Grimwald:
The whole series was a dream Billy Raven had or took place in his imagination as a way of coping with his terrible circumstances. Lord Grimwald symbolized Harold Bloor. He was never a real person, or, if he was, he only visited Bloor’s once.
I am a truther for a lot of things, but my biggest truth is that Dagbert is agender. Why? If Lord Grimwald had no first son, then Lysander could kill him all day every day no problem. He/They Dagbert who doesn't identify as a man or son or boy but actually just doesn't care