We knew that he was dishonest but we didn't imagine he would sink so low as to steal from his own family. (*) behave so disgracefully (*) behave so stupidly (*) behave so clearly (*) behave so fully
This is a companion discussion topic for the original entry at https://english.best/questions/23649,we-knew-that-he-was-dishonest-but-we-didnt-imagine-he-uwould-sink-so-lowu-as-to-steal-from-his-own-family/