There are a total of five members of the Akai family: the mother, Mrs. Akai; the deceased father, Mr. Akai; the youngest daughter, Masumi Sera; the unknown son; and the eldest son, Shuichi Akai.
Shuichi Akai is the eldest son. He is the best of the FBI Agents; the boss of the Organization and Vermouth nicknamed him the Silver Bullet. Akai is said to have had died at Raiha Pass on Friday the 13th in Detective Conan episode 504 English subbed. There are theories that Akai faked his death with the help of Kir and Conan and created the alias of Subaru Okiya. He resembles their mother.
Masumi Sera is the youngest of the Akai siblings. Her name was formerly Masumi Akai but was changed to her mother's maiden name. Sera transferred to Teitan High School to investigate her brother's death in Japan. She is often mistaken as a boy. She resembles their mother.
There is an unknown middle brother. He is apparently still alive. There are many theories on who he could be. He doesn't look like his siblings. He resembles their father instead.