Hey! I would word it as follows : I went to see "classical theatre" at the Merida Theatre. I saw actors performing at the theatre . Their performance was great.

"I went to see classical theatre to Merida theatre" - replace the 'to' with 'at'. - when you see something at a theatre you would say I went to see a 'play' or 'performance' instead of 'theatre'. - so in summary: "I went to see a classical play at Merida theatre." " I saw actors acting a performance" - 'actors acting' isn't technically wrong but doesn't sound right, it would be better to say 'actors performing' - replace 'performance' with 'play' because 'actors performing a performance' would also sound awkward - in summary: "I saw actors performing a play" "I saw actors performing at the theatre" - this is fine "They acted very well" - this is fine, though you might prefer to say "they performed very well" "they did a great performance" - this doesn't sound right, because its not correct to say they 'did' a performance, you would say they 'put on' a performance - so you would say "they put on a great performance"