Twin Movement

I am 24 weeks pregnant with fraternal b/g twins. I am getting more & more concerned. I feel Baby A moving A LOT. He is very active. Several times a day. But I barely feel Baby B. She makes her appearance known maybe a couple times a day. I had an ultrasound at 20 weeks - anatomy scan. Everything looked great. Heartbeats were strong. Is this normal?  Could it be positioning?  Any advice would be appreciated!  Thank you.