Family ties

Assalamualaykum Mufti

I need advice. My sister from overseas is getting married. We are invited to the Walemah which I was told is at restuarant, which serves alcohol. I am not happy to attend this aspicious function at such a resturant as i believe it is haraam and I feel there are plenty of halaal options. What can I do to prevent affecting family ties with my family and with my future brother in law.? Your advice and guidence will be highly appreciated.