The concept of praying together comes up many times in the NT. Just wanted to know, is it asking all the disciples to pray at the same time or be together and pray one by one?

1 Cor 14 indicates that we are to wait for each other. While we might all sing at the same time – same words, same piece of music – if we all pray at the same time, there will be chaos. (Unless, of course, we are reading/using set prayers.)

Short answer: one by one. True answer (in the spirit of Acts 1:14): we can pray in groups, but this assumes one person is forming the words. It's a matter of courtesy.