Why does the Torah change the expression from "v'Ish asher Yishkav... " to "v'Ish asher Yikach ... "?
Why is the first of the two women Chayav Sereifah? Did he not marry her b'Heter?
Rashi #1: The Pasuk is speaking where he married his wife, then her mother , and then her mother's mother. The last two are both forbidden.
Rashi #2: "Es'hen" means 'one of them'. 1
Rashi: Because 'Hein' is Greek for 'one'.
How is the burning carried out?
Targum Yonasan, Sanhedrin 7:2: By pouring molten lead down the throat.