I need to know if and why aggrandizing his family to the thrones of conquered nations was beneficial to Napoleon and his Administration.
It was a good idea but Napoleon did not take into calculation the corruption, treachery, and incompetence of his siblings. His brother Joseph was a poor choice for Spain, he was a terrible military commander and fled the capital anytime an enemy army came near it. Louis was a decent ruler of Holland but put Dutch interests over French interests which irritated Napoleon. Jerome actually did alright being king of Westphalia and set a decent example for other dependent states to follow, his one problem though was large spending on his extravagant lifestyle. Napoleon’s sister Caroline married Joachim Murat and in 1808 Napoleon made them king and queen of Naples. They showed their appreciation by betraying Napoleon in 1814 and siding with the allies. Napoleon’s other sisters were giving minor territories but nothing important. So overall it was not beneficial to Napoleon to give his family thrones across Europe, they were either incompetent or disloyal.