Confessing we're an adoptive family when first mom is present

I have 4 adopted from foster care kids, all older, and we visit regularly with their first mom and little siblings. We are often out in public. It does look confusing, I'm sure. Espec. with the different ethnicities. All the kids call me mom or mommy, and her ma, mommy, or mommy N. People often make comments about the kids when we are out and about, I'm sure appearing to be one big happy family... it's just there are 2 moms. So I figure people assume first mom and I are partners. Doesn't usually bother me.... but sometimes I wonder how to delicately answer when asked questions. Last week at a McDonald's, a worker was acting extremely sweet with the kids, we were celebrating 2 birthdays and the kids were all excited. She asked if we were all family, I hesitated, noticed my nearly 17 yr old looking at me as though she did not want me saying the truth. I just said, "yes, we're family", and left it at that. That worked that time, and probably will other times. But there might just be sometimes when I do actually want to talk to someone and acknowledge our open adoption, without any negative comments about first mom. I do sometimes get asked questions about it when the first mom is NOT with us, and the kids don't mind me saying some of them are adopted. It's either that, or I slept with several different ethnicities and had babies with them!! LOL. My teen daughter is just going through a period where she feels protective of her first mom, and I understand that. SOMETIMES, I just wanna be able to say "we have an open adoption". If any of you have been in my kids' shoes, or can imagine if you didn't have an open adoption, what would YOU want me to say??? Should I NEVER confess we're a big family through open adoption if first mom is present??