Re: should I be offended?
You know your sister well because she’s family. Your interactions with your BIL for the most part may have been positive. But since you don’t live with them 24/7 you don’t know what goes on between them…their discussions/feelings about certain issues. So can you really confidently make that claim? Unless your sister is miffed at you for something that you may have done or said in the past (which you may not be aware of)…I don’t think it’s an unreasonable possibility that her decision could be based upon her husband’s feelings or even her attempt at making things comfortable for him when she goes on her trip.