Can you talk directly to the wife to ascertain if anything has really changed? The ground rules really won't help if she has not embraced the idea. She can abide by then and still make everyone miserable.
And I am not clear that her husband ever presented the nature of the relationship between you two honestly to her - before you were invited to stay the first time. So from her perspective, it probably was a surprise. She probably felt she had signed up for one thing and ended up getting an entirely different situation. While I don't think you and your guy actively sought to inflict pain on her, imagine how you would feel if you were in her shoes.
Now if she truly wants to try polyamory, yes, there is hope. However, if she is doing this out fear of losing her husband if she doesn't go along then it won't work.
Last edited by bookbug; 10-11-2013 at 12:05 PM.
Reason: Additional thoughts