You can add this group @[email protected] from Mastodon and see and interact with all the posts. Mastodon doesn't (of course) have some of the functions, like threading, upvotes/downvote etc, so the experience might not be as good.
Similarly on Kbin, you can follow people from Mastodon - their posts end up in the Microblog section
on mastodon you can follow people from lemmy and kbin, yes
in the searchbox on mastodon search this:
@coremeltfx
and you will find your kbin user with the replies and content you wrote. but since mastodon and kbin are different it will not work properly (for example following kbin magazines in mastodon won't show the content on those magazines)
But since kbin and lemmy have the same purpose their interoperability is good