Hi,
Good for you for your 30 days sober.
For me, I did not want to tell people around me, that I had stopped drinking. I felt that it was an intensely personal decision. I tried lying, making up excuses, a couple of times when I was out at dinner with people who were drinking, and I hated it. I recognized that for me, honesty in sobriety was hugely important. I decided that 'No, thanks', was sufficient.
I agree that having a plan is a good idea. Can you avoid the girls drinking part of the weekend and maybe help with dinner preparations, or something like that? Could you excuse yourself and go for a walk?