I belong to a Tehillim group online which says the whole book of Tehillim daily, and in prearranged form, on Shabbat and Yom Tov, bli neder. For those days, the large group is divided, ahead of time, into smaller groups, so several entire books can be said simultaneously. One of the groups is asking us to take chapters that just became available. It so happens that they are some of the chapters I already say for my group. My question is: when I say my chapters for my group, can I have the second group in mind, as well, or do I have to repeat the chapters for the 2nd group? It takes me several hours to say my 42 chapters, and I don’t think I can take upon myself, bli neder, to repeat any chapters.

It's no problem having both groups in mind.