Is it permissible to sit with a profligate person after admonishing him, especially if he is a relative?

If a transgressor insists on their disobedience after being reproached, the fundamental principle is that you should leave their gathering. Their kinship does not justify sitting with them while they disobey Allah. Ibn 'Uthaymeen mentioned that sitting with people who commit evil, when one is able to leave, is a participation in sin, based on the Almighty's saying: "And He has already revealed to you in the Book that when you hear the verses of Allah disbelieved in and ridiculed, do not sit with them until they enter into another conversation. Indeed, you would then be like them" (An-Nisa: 140), unless there is harm in leaving.