Re: Yizkor Book
It looks to me like a "topic" is simply a new thread of discussion created by a member, rather than a "Forum" where all messages about a particular subject would be housed. I am not sure if this application gives the admins the ability to create forums but if it does, then "Yizkor Books" should be a Forum (rather than a topic) where users can send messages related to that subject but not necessarily have to respond to the person that sent the original message.
In the present state, it looks to me like all one can do is respond to the individual post from the person that created a topic. So in this particular case, Binny posted a topic about Yizkor Books and all we can can do as users is to respond to it as if we were in a discussion We do not have the ability to create another topic within Binny's topic. If I want to create my own topic on Yizkor books it will become a new thread.
So, I would ask the moderators/admins to look at the structure of this application to see if "Forums" can be created where all threads of discussion about a particular subject would be housed.
Here is an example of a Discussion Group Application that allows the admins to create forums: https://www.jitbit.com/asp-net-forum/
Hopefully this makes sense!