See... I always assumed that they were two mirror worlds with a thinned veil in between. One was modern and had all the comforts and technology of now (a link to the mortal world) and the other side of the veil was the old castles, magic, and no modern tech. That would explain why Thadius was a modern world and Antul, where Lucilius lived, wasn't so modern.
I'm on board with there always being a struggle. It makes sense for the two families to always be at war with each other. They probably want to wipe each other out and that almost happened with the Merhites.
Your second point would make sense if the point I made above was true.
The point of their father's death seemed to be just something to springboard some anger between the families. I think having a hatred as old as the families themselves is way better. No one knows why they hate each other and so they just continue on with it, because that's what they've been taught and it's all they know.
I thought I had more to say, but I need to get to bed. Work again tonight.