I am supervising a PhD student, enrolled at another University, where the co-supervisor is employed. We developed some useful software in her thesis and published 3 papers. In this development another member from the other university also participated. Now she will defend her thesis and leave, and it is not clear yet whether they will be interested in further development of this software.
I am really interested in this and I am the only one who knows how to use it in different contexts so I can foresee that I could get 30 publications with this tool in the next 5 years. I have the feeling (and I could obviously be wrong) that since the PhD student will leave, the colleagues from the other University will not work anymore on improving the software. But if I get new publications with the software, they have the right to be included as co-authors on all the papers even if they do not anything at all.
We are friends and we work together very well, but I think this is unfair. And I do not know how to present this situation to them. If I tell them exactly like this I feel they will get upset. So I am lost and I do not know what do here. Most optimal situation I can think is that on each new paper, tell them that I need to add some minor features to the paper (so that we work) and then I can feel they have the rights to be co authors of the paper. Are there better ways to handle this? I feel that we should have settled everything from the beginning, but it is now when I realize about this.