When there are two authors, separate their names with ‘and’ rather than by an ampersand (‘&’). If there are three authors, separate the first and second with a comma, and the second and third with a comma and ‘and’.
E. Heffes, M.D. Kotlik, and M.J. Ventura, International Humanitarian Law and Non-State Actors: Debates, Law and Practice (The Hague: T.M.C.Press, 2020).
If there are more than three authors, you may list the first author and then ‘et al’.
‘Op. cit.’ should be avoided. ‘Ibid.’ is used where there are two or more consecutive references to the same work.
Subsequent references to the same document could be: Author last name, supra, at page number.