Does Shaking Hands with Sister-In-Law Break Wudu?
Question

Is it permissible for me to sit with my wife’s sister, and does it break my wudu if I touch her?
Please advise me, may Allah reward you with good.
Praise be to Allah.Can you sit your wife’s sister without mahram?
“It is haram for you to sit with your wife’s sister or any other non-mahram woman on her own. The Messenger of Allah (peace and blessings of Allah be upon him) said: “No man is alone with a woman but the Shaytan is the third one present with them.” (Narrated by al-Bukhari, 9/290; Muslim, no. 1341; Ahmad, al-Musnad, 1/222 and 346)
 It is haram for a man to be alone with a woman who is not his mahram . Your wife’s sister is a stranger (i.e. non-mahram) to you, because if you were to divorce your wife, it would be permissible for you to marry her (her sister). So she is not one of your mahrams.
Does shaking hands with sister-in-law break wudu?
With regard to breaking wudu, it is only broken by touching a woman with desire. If a man touches a woman with desire , this breaks his wudu, whether the woman is a non-mahram or otherwise. The kind of touching which breaks wudu is physical touching with no barrier in between. This is what has been stated by the scholars.” (Fatawa Shaykh ‘Abd-Allah ibn Humayd, p. 48) 
For more, please see thee answers: 38153 and 12663
And Allah knows best.