What is the ruling in Sharia on greeting the mother of one's wife and kissing her on her cheeks and neck, and what are the proofs for this from the Qur’an and the Sunnah?

It is permissible to uncover the face for someone arriving from a journey, but kissing the mouth is not permissible for fear of arousal. It is permissible to kiss the head or forehead out of respect, as long as it does not arouse desire.