No, it won’t. Really, the developers of Lemmy are not assholes, they do a great job. Unfortunately I can’t tell the same thing about the developers of a fork that don’t work well and isn’t Fediverse.

Don’t know about that, not a coder, but Lenny should be very similar to Lemmy, so I don’t see the federation between both shouldn’t work.

The only one I know is derpy.email, they apparently federate with lemmy.cat and they pretend they federate with lemmy.ml. Just make your own server, you must have a lot of followers on Mastodon to join in.