My family had a kinda similar situation. My DGAunt married her niece's DFIL. That meant that her DGNiece & DGNephew became her DGK's. So when her nephew/grandson got married his brides family were so confused! Sometimes he called her Grandma & sometimes he called her Aunt N****. Well a few months after the wedding DGA got very sick. (She had sepsis!) I went to the emergency room to be w/her. I told a security guard that I wanted to see my Aunt & her name is N**** P******. While the security guard was escorting me to the room she asked me if my Aunt was related to (she named the nephew/grandson.) When I said yes she asked how she was related & I just stammered for a minute. Then I said that it is too complicated to tell her right then. I'd explain once I had seen how DGA was doing. An hour later she came back in the room & told us she is now the DMIL of the nephew/grandson & was confused. So we explained it too her & we all had a good laugh which was just what DGA needed right then.