I am the "in the Family adopted Son-in-law"

Yoshihiko, who works for an insurance company, marries his girlfriend Saori and is adopted into the Ryujin family, an old and wealthy clan. However, during their honeymoon, the company goes bankrupt, the Ryujin family's assets are seized, and the entire family is forced to move into a small house in the suburbs. In order to support Saori, her mother-in-law Ranko, and her sisters Shiori and Kaori, Yoshihiko works hard as the family's sole breadwinner while trying to be thrifty. But his mother-in-law, who is used to a life of luxury, continues to make all sorts of unreasonable demands. Eventually, after seeing Yoshihiko's hard work and struggle, Ranko recognizes him as the new head of the Ryujin family, and entrusts him with the revival of the family fortune. (Source: Wikipedia, translated)