What is the ruling on a wife's paternal uncle kissing the women of the family, and is it permissible for him to kiss his mother-in-law in front of others?

Shaking hands with and kissing non-mahram women is a reprehensible act (munkar). Whoever commits it must perform sincere repentance (tawbah nasuh). And whoever witnesses it must advise the perpetrator and explain the proofs that forbid such actions.