A little background, DH and I have a flatmate. He is an old old friend and is practically the third person in our relationship. He is like the third parent to my children and I trust him with their lives in a heartbeat. He was with us throughout the home study and took exclusive care of our first two DC when we traveled to Pakistan to adopt DD2. He is part of our family completely.
My DB and SIL are coming for holiday near us and plan to spend at least one weekend of the holiday doing couple things and rekindling their marriage. their DC (4 and 2) were supposed to stay with us for the weekend. SIL has changed her mind upon discovering that there might be situations where our flatmate would be left alone with the children. She has known him (through us) for almost five years. She knows how close our DC is with him. We'd already planned to have them for the weekend and had rearranged our plans. Both DH and I will be home all weekend as well. Our last house was a duplex and had a small studio apartment that our flatmate lived in right over us. We have since moved to a different house in which flatmate has his own bedroom but is in the main house with us. SIL says she is uncomfortable leaving children with us now because we have a "strange man" living in our house. FFS he is not a "strange man," she KNOWS him. He has been here since before our DC and will be here till he decides to move out. He is practically a father to our DC, they love him and he them. We have already changed our plans to accommodate them and now they're going back on it and (it seems to me) insulting our friend and his relationship with our DC in the process. AIBU to be offended or is she being unreasonable about our family setting?