Uncharted territory

My ds 9 gets pictures taken at bass pro every year. This is the first year separated, I made the appt for the pictures. My stbx in laws will be there, and I got this text from my stbx: "Mom bought Santa picture clothes and may be sending you pictures of them later when I drop him off. Just thought I'd let you know"

I feel as though my stbx MIL should have asked if she needed to get clothes. Now I feel obligated to accept these clothes to not start an argument.

What should I do?