I know this probably doesn't belong on this board, but it's my favorite one

Anyway, I am not planning my wedding yet because it's so far away, and I kind of just want to enjoy being engaged at the moment. But my fiance (does FI stand for fiance on these boards btw?) and I already know who will do our wedding cake. This woman has done every birthday cake for every person in his family for the past twenty-ish years, as well as his mom's first and second (remarried) wedding cake, and his aunts' cakes, and his grandparents' 50th anniversary cake. Since we have been together (since Oct 2005), she has done my birthday cakes. Basically, she's doing our cake, end of story, and we both agree on this.
The problem: my family has only had her cake on a few occasions, and they want me to consider other people too. My mom and stepmom even think I am "missing out" on all the "cake sampling fun". How do I tell them that this woman's cakes are amazing, and beautiful, and we both want her to do it? I have tried explaining that we aren't planning our wedding yet, and when we do start, we already know we want her to do it, but they don't understand. Help!