My fiancé has two sisters, both who are extremely on and off with us. At times they are sweet, mostly if they need something, most times they are distant and catty and have caused a ton of problems. They don’t even remember our daughters birthday. We’re getting married next year and can only have 18 guests, we are considering just not inviting them, since there’s a 50/50 shot they’ll do something petty or say something shitty just to upset us or cause drama. We know this is a big deal, but we don’t know what else to do. If we try talking to them they claim they have no idea what we’re talking about. Advice?