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A. Ladies and Gentlemen, we have a suprise guest. It's Simon and Garfunkel.
B. Ladies and Gentlemen, we have suprise guests. They are Simon and Garfunkel.
C. Ladies and Gentlemen, we have a suprise guest. It's John and Edna.
D. Ladies and Gentlemen, we have suprise guests. They are John and Edna.

On the phone...
E. Hi Superman. This is Batman and Robin.

F. Hi Superman. These are Batman and Robin.

G. Hi Superman. This is Chris and Joseph.
H. Hi Superman. These are Chris and Joseph.

Which of the above sentences are correct?

In my opinion, we can use 'is' if the persons are popularly known as one duo or team like A and E. However, 'are' is used if the persons are not known and popular like D and H so each person is treated individually not as a group or team. I'm not sure about this, though. Would you say B, C, F and G are incorrect then?

Thank you.
Comments  
No, although it is OK for 'bread & butter', it would be rude or unobservant to refer to people in that way.

B. Ladies and gentlemen, we have surprise guests. They are Simon and Garfunkel.

D. Ladies and gentlemen, we have surprise guests. They are John and Edna.

On the phone... Not possible with both unless it is a conference call which connects simultaneously with both fictional characters. Hi, Superman. This is Batman. Robin and I are throwing a party tonight, and we wondered if you'd like to fly in. But in any case, 'these are' is not used on the phone no matter how many people are connecting.
Thank you, Mr MM, for your answers.

What if it's a indeed a group composed of more than two persons e.g. Scissor Sisters, can I use the 'is'?

Ladies and gentlemen, we have suprise guests. It's the Scissor Sisters.

Also in a conference call, can I say "Hi, Superman. This is Batman, together with Robin"?
What else is correct to usually say to let the person on the other line know who are in the call?
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Yes, those work OK. 'The Scissor Sisters' I presume is a group name. Your Batman quote seems fine, too.

I don't know what people really say at the beginning of a conference call, since I've never experienced one, and I don't know how they hook up, technically or chronologically. I presume that each person introduces himself.
OK, thank you for that clarification. Since those work OK because it was a group name, shouldn't I have said the following to be consistent with singularity?

Ladies and gentlemen. We have a surprise guest. It's the Scissor Sisters.

Or is 'suprise guests' OK because it refers to individual members of the group, therefore plural?
I think the natural reaction of the announcer would be to think of them as several girls.
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Therefore, below is still the most appropriate one. Thank you so much for your assistance.

Ladies and gentlemen, we have suprise guests. It's the Scissor Sisters.