I don’t know where exactly to post this question but there are two communities on two different instances. Are those same?
If not there can be n number of such communities on any instance how to get saturated content if them all? Is there better alternative than lemmy?
On the desktop version of Lemmy I believe it lists the instance along with the username.
If you are worried about users using an app like Jerboa not being able to tell the difference you could rely on things like a unique profile picture or PGP signatures. It all really depends on your threat model.
It would be a lot of work to do anything more than cross post your content.