I.. I had to try and draw the twins when they were little. HAD TO. This is probably them at their most innocent.. they grew up pretty fast. @__@ Yes, Carmen picked on Adrian and not the reverse. She's technically the older twin being born before her brother.
Adrian hated when their father or older sister stepped in because even though he usually lost, he did like to challenge Carmen and keep trying to win against her. Carmen is like her sister (Maria) though; they've both got quite a domineering streak that was evident even when she was little. xD
Nowadays Carmen and Adrian are quite different [still identical in appearance other than the male/female difference], but they do share a bond and still have moments like this where they find themselves on the exact same spot on the same page as one another, whether they like it or not.
-- About 30 minutes for the sketch; 3-4 hours lining/colours (PS CS2)