the interlopers chapter 33 what personal factors keep this feud going?

The major factor is the land dispute. They also disliked each other:

The neighbor feud had grown into a personal one since Ulrich had come to be head of his family; if there was a man in the world whom he detested and wished ill to, it was Georg Znaeym, the inheritor of the quarrel and the tireless game snatcher and raider of the disputed border forest.