How the meeting is organized is extremely important. If it's efficient, then it's more welcoming. Unless I'm misunderstanding, as you have it set up now, you have 2 or 3 authors present 1 to 2 chapters once a month, and then you discuss. How long are these meetings, and how much time is left for providing feedback and discussion? After my full time job, I only have so much time in a day to commit. Additionally, if you have more than 3 members, it could be up to two months until you receive more feedback.
Thinking back to college writing classes, our homework for critique days was to read our peers drafted work, then come to class with our feedback. We'd spend the hour discussing up to 10 drafts. I think this is a very effective format for a few reasons:
* Presenting aloud is intimidating - I am yet to be confident enough to present what I've written aloud, so any group that presented that way would be far too intimidating for me to join. 487
Maybe more seasoned writers would be okay with this, but to be more welcoming, consider having your members post their drafts on a shared for the upcoming meeting. This also allows new members to backtrack on existing members' work, as well as post their own for review ahead of their first/second meeting.
* Time - You could give a stipulation to post whatever work has been completed a week beforehand (be it a paragraph or a chapter or two - the time individuals may have during a month to write can vary, post what you have). Then, you could provide feedback for each author, more frequently. You'd also have more time during that meeting to have more in-depth discussion for each author's work. (Time is limited, and while reading the work ahead of time takes time, it's more spread out, and you can read that author's work when you get a chance the week before.) This also gives new members access to go back and read what's been written before in the time they are able (even if it's just catching up on one each month).
* Preparedness - By reading the work ahead of time, you have more time to mull it over and think of constructive feedback. Maybe go the literal class-like route and do a write up (for the author to go back to later). I'm also one of those people who's slower to think. I provide my best feedback when I can take time to consider something, instead of having to respond immediately after having heard the content, and I think best while writing (which is why I write). 487