How can my students work on a pages document from two or more iPad Minis in real time?

I am wanting my students to create charts, graphs, newsletters and posters using Pages on my iPad Minis that I received in a grant. I would like them to create one document and be able to edit it from multiple machines in real time, very similar to Google Docs. Two of my students were able to do so, but they were using their PCs and on the website www.cloud.com. What gives?

Thanks!