This is the 18245th most frequent Russian word.
членам
"Членам" means "to members" or "for members" in English.
Here, 'членам' is in the dative case plural of 'член', meaning 'members of', and is used to indicate the indirect object of the action (those who were given an opportunity to speak).
На собрании предоставили слово всем членам организации.
At the meeting, everyone in the organization was given a chance to speak.
In this sentence, 'членам' is again in the dative case plural of 'член', used to refer to recipients of the action (those to whom the book will be interesting).
Книга будет интересна всем членам группы.
The book will be interesting to all members of the group.
Here, 'членам' is used similarly in the dative case to indicate recipients of sent items (club members).