Hi, I'd like to help you with your question.
You mentioned that your sister does not like your husband's family. You also mentioned that she does not like your brother's girlfriend. It seems there are a lot of people in this situation that she does not like. And from your description of how you've tried to handle this, you have made more than adequate accommodations for you sister's feelings. It sounds like you are more than flexible, which would prove you are not controlling. It is ironic, but it seems your sister is more controlling about the situation than you are. She refuses to cooperate if circumstances are not to her liking. She tries to get you to have separate holiday events and wants only certain people to participate. That is controlling behavior and completely opposite of what you are doing, which is trying to help improve the situation.
Have you asked your sister why she does not like your husband's family? Is it something they did that may her uncomfortable? If she cannot come up with a good reason or is unwilling to work with you on whatever the problem is, then the problem is with her. Most people are going to have some things they do not like about someone else. But in order to get along in society, most people learn to cope with the bad in order to be together for the greater good. So unless your sister has a good reason (your in laws drink, cause a ruckus, abuse others, etc), then you are not the problem, she is.
This problem may continue unless you stand up to your sister. Let her know that you will invite whomever you want to your get togethers and she is invited as well. Then let her make the choice about whether or not she will attend. She may get angry about it because it will take her control away, but it will make it easier for you to host holidays.
I hope this has helped,Kate
I haven't heard from you. Did you have more questions or want clarification?