The unexpected tradition.

So the idea mostly goes. My character is a futanari who has married her dream girl, and is going on their honeymoon right as they're leaving the wedding. What's unknown to my character is that my new mother in-law is joining us, and I don't find out until we're at the resort. Although it's wasn't anything bad it's just according to the traditions they follow a mother must have sex first with her daughter's partner, and then after teach her daughter how to properly pleasure her husband/wife.