RobH_en_tn/2ki/10/03.md

set him on his father's throne

Here, sitting on the king's throne means to be appointed as king. AT: "make him king in his father's place" (See: rc://en/ta/man/translate/figs-metonymy)

for your master's royal line

"your master's descendants." Here the man that they selected to be king is referred to as Ahab's royal line of descendants. AT: "to defend your master's descendant" or "to defend him" (See: rc://en/ta/man/translate/figs-synecdoche)