I'm almost 27 weeks and ALWAYS feel more movement on my right side, than on my left. I did learn that one baby is more posterior than the other, so maybe I feel the one who is closer to the surface more. Also, I feel like I know which baby is which, and have since feeling movement. However, I have read that many mamas have felt the same, then saw during an ultrasound that the "less active" baby was actually adding to the movement they attributed to the "active" one. So who knows there! I do know that babies can change roles, such as B being the one to present first, (as A usually takes that role), but I don't think that they can actually change sides. At least that's my impression.
I do think that baby B is able to squirm a lot more and try to get comfortable. Baby A has been vertex for a while, so she has her comfortable position, but I felt B going to my left ribs last night (she can lie above and transverse). At least I think that's what's going on. Also, I was not feeling movement on my left side and began to slightly worry. I happened to be looking down at my belly and saw my shirt "jump" on the left side. I didn't feel it, but there was sure movement! So, who knows! Hope this helps