Joining actors are several who have appeared on the stage before.
Above seems OK? semantically?
No it isn't.
And... Who are joining actors? what does it mean..
Thank you in advance..^^
An interpretation of that sentence would have to be a guess.
"Joining actors", no doubt, are actors who are joining something.
It could mean something like: "Several of the actors who are joining us have appeared on the stage before".