My fiance has two sisters. I get along with them both however I know the first (H) better than the second (K). H and I have traveled together twice (with our signifigant others) and have become friends. K and I talk but we've never seen each other outside of family parties. I'm having a small party, she'd be the only attendant besides my MOH. My fiancee is afraid that if I ask H then K will be mad.
Quick notes: K is 50, married to a bigoted jerk and has three spoiled daughters. H is 47 and her husband is easy going and the kids are great. K is also very high maintenance and likes to run everything.
What is the etiquette? Do I have to include both sisters? If that's the case then I won't ask either. I don't want to cause drama. Any advice would be appreciated!