The Genius Prince's Guide to Raising a Nation Out of Debt (Hey, How About Treason?), Vol. 4 (light novel‪)‬

IT AIN'T EASY BEING A GOOD BROTHER!
It's time for the three Imperial princes to meet and argue their way to the throne in the city of merchants, Mealtars. Sounds like a good opportunity for Wein to take a breather since this gathering obviously has nothing to do with him...until Imperial Princess Lowellmina goes out of her way to invite him to Mealtars, too. But Wein's already learned that it's always better to decline her offers. Turns out, things would have gone smoother if he'd just attended, because now he has to deal with a whole new problem: his sister, Falanya, going in his stead!