Short answer: there is probably no universal answer; in other words, you should check with the journal to see if there is prior precedent or guidelines in place. More specifically, you can check with: (1) the author instructions [it would be surprising if nothing is mentioned or this has not come up before], (2) the relevant section of a variety of recent, previous papers published by the same journal with a suitable number of authors, (3) an editor at the journal. From at least one of these options it should become clear what is expected of that journal for its author bios.
Aside from the specific journal, we could also more broadly consider the purpose of an author bio. It is important to preface such a discussion with the disclaimer that many journals don't even bother with such anymore in these days of Google, institutional webpages, and so forth. However, leaving that aside, we could consider that the author bio serves some of the following possible purposes:
Identify conflicts of interest: Were any of the authors employed (in some capacity) by a company whose profits could benefit from the results published? While such CoI's could sometimes be established from the institution, sometimes they could arise from secondary sources of income. Were, for example, some selection of authors paid for consultancy at a pharmaceutical company whose product could benefit from the new results? Did they serve on the board of a committee with a certain stance on a certain topic?
Establish seniority and background on the authors: Were the authors students at the time of publishing the paper? Or were they professors? Which authors held which positions? What is their main area of expertise or qualifications in said areas? Though such information should of course not affect the interpretation of the results of the paper, it may be useful to establish, perhaps, for awards purposes, or just to satiate the curiosity of the reader.
Contact information or disambiguation: If not already given elsewhere in the document, additional information may be necessary such that individual authors could be disambiguated and/or contacted by readers.
As mentioned at the start, admittedly the importance of author bios has declined in these days of the Web.
In summary, check with the journal guidelines, previous papers and/or editors to see what to do. My guess would be that you should include a brief bio of all authors with their institutions, roles and duration of employment at those institutions, and other paid or volunteer positions (past or present) that may affect (or be seen to affect) their impartiality in the context of the results of the paper (if applicable and not given in a dedicated CoI declaration). If there is space, you could include the principal areas of interest of the authors. I would imagine something along the lines of:
A and B are PhD students at the University of Z. C is a Professor at the University of Z, chair of the Institute of Y and part-time consultant for X. D is a Postdoc at the University of W. E and F are Masters students at the University of V. The principal areas of research in which the authors have worked are L (A, B, C), M (C, D, F) and N (E).