-DELETED- Attending a family gathering including a same sex couple

Should we attend a family gathering where a same-sex couple are planning to be present? My sister-in-law is currently married to her partner. We love both of these ladies but have made it clear that we don't support their lifestyle. There's a huge family reunion next summer and my husband wants us to go. I want to go too, but we have three children, and I don't know how it will affect them. What should I do?