My father remarried when I was young and growing up my step-mom was like a second mother. However, they ended up having a messy divorce and since then my father has remarried again. My previous step-mom moved to a new town and remarried, and while I am on good terms with her and her daughter and I keep in contact with them, the relationship has faded some over time.
My father has requested that I not invite my previous step-mom and her daughter to my wedding. I am now in a sticky situation since I had already sent out the save the dates many months ago and I am currently preparing the formal invitations to send. I had hoped to invite them, and several years ago I had even attended my step-sister's wedding. Since he is contributing financially to the wedding and I want to avoid drama, I told him I would try to honor his request.
How do I politely explain the situation to my step-mom's family? Would it be acceptable for my fiance and I to host a mini-celebration with just them?