We heard in a majlis, that if we take out somthing for sadqa on 12th Imam's name, we can only give out that amount/thing to a syed/syeda. Can we not give it to anyone else?

This is not true information. You are free to choose who you give your donation in the name of Imam. What’s preferred is to give to the lover and follower of the 12th be it Sayyids or non-sayyid