Hi - It's going to be one of those moments that no matter how much you think and prep, for there's just a lot that won't sort itself out until there you are.
First, be who you are. It won't help to be less than that up front.
Second, that said be tasteful and moderate (whatever that means to you and you are the only one that counts here).
Third, regardless of how things go you are a great and beautiful human being. Bring love with you when you see them and leave with love in your heart. In the end, love is all that truly matters over time and your love is all yours to have and show - it's what makes you and all of us such beautiful beings when we offer it.
Several of my first discussions were difficult (I wasn't so loving) and some were magical - I couldn't predict. Still, I'm glad that I had them and everyone that was important to me and still is today, even if some relationships are distant and largely quiet - I can love unconditionally and always try to. It's so much better than the alternative.
Take good care of yourself and go as the loving child of your parents . . . best of everything to you and yours,
Rachel