Cousin, I adore you, but a simple 'we were busy' really would suffice. Trust me. I would understand.
I will, however, take care of the party, and the two of you will have to indulge me at least for a little while. Toasts must be made. You won't deny me that not that you will have a choice.
Why don't you both hyphenate? I think it would show proper respect for each other and the bond.