Only receiving emails by using newParticipants of Post

Question

Hi,
My team is using ms graph group,conversation/thread, post api to create a forum like web app.
We're trying to create multiple threads which can have different recipient collection(hopefully by using toRecipients of thread) in the same single conversation, although not sure if that's achievable.

The first issue we met: if to use toRecipients of Thread to create thread/post, the recipient cannot receive emails. This is a big question mark to me at the moment.

Then we tried using newParticipants of Post to create thread/post (feels an uncomfortable workaround to me), the recipient can receive emails by doing this, but it can sometimes create new conversation and thread for the new post if setting different recipient collection to newParticipants, which is not ideal as we want to keep all threads in a single conversation for the group.

Sorry that I have more than one question:

1. Is it possible to have threads which toRecipient are different, but in one single conversation
2. For the first issue, not sure if there is an easy way to solve?

Rob
Thanks