Greg responds...

1) The Sisters used the events of "City of Stone" to weaken Macbeth and Demona's wills. They took them at extremely vulnerable moments when they willingly abandoned control of their own destinies out of despair. It's a tiny loophole, but that's all the Sisters needed. As I'm sure you've noticed, Oberon isn't exactly a stickler for the letter of the law.
2) Jeff, I'm not entirely sure. We were a long way from any equivalent to Goliath being an "in-law". Goliath and Elisa had not even discussed their relationship. They'd never even gone out on a date (though they'd certainly had some romantic moments). I don't like to plan characters emotional responses too far in advance, but my gut reaction is that the guy who would have the most trouble with it would be Derek. Beth would get it. Peter would be wary. Diane would want to make sure Elisa fully understood what she was sacrificing. But I think Derek might have a real problem with it.