I had my first belly roll from the twin on the right around 15 weeks.

I didn't feel the left twin move till much later, although the left twin's placenta was at the front and the right was at the back. So the placenta was blocking a lot of movement from the left twin.

Do your twins share a placenta?? Do you know where the placenta is?? Placenta's at the front will generally hide any movements for a little while, but don't worry once they grow bigger you will feel lots of movements. I found that with my twins one would be very active, while the other slept and then they would swap around. The strangest sensation is that depending on where they are positioned you will only feel movements in one area of your belly, where with singletons you will feel the movements all over your belly.

Because my guys pretty much stayed side by side for 95% of the time, I would have one half of my belly move around and then the other half would move independently. I found it reassuring that they were positioned how they were as I always knew which twin was moving around.