I took on (bli neder) to learn part of mesechet eiruvin for a person who was niftar. A friend of mine had also committed to learn the same part for someone else who was niftar. We decided it would be a good idea to learn together.
The intention is that separate siyumim hasahs will be made on the yartzheit of both the people who were niftar, and our learning of the part of mesechet eiruvin will count towards them. Is it ok that we are learning it together or as it is for separate people do we each need to say every word of the gemara for the siyum to be ok for both the respective niftarim?
You can both make a siyum even if you didn’t speak out every word. A person can make a siyum even if he only thought the mesechta.
Kovetz Halachos (Pesach) 13-14, ftnt. 17, Yoma Tava L’rabonon 2-4.