Singular or plural

2 is correct. The subject is "their names", not "what".

Yes, but instead of saying their names are Fred, CJ and GG, I can say:

Fred, CJ and GG are their names.

In this case, what is the question for Fred, CJ and GG?

What is their names? or What are their names?

If both, what is the difference in

Fred, CJ and GG are their names.

What are their names?

I hope this helps.

It is still 'What are their names?'

So, return to my original question:

Would you say (1) or (2) or both? Why? (in that case)

1. What is their names?

2. What are their names?

If both (I think (1) is also correct. How about your opinion?), what is the difference in meaning between them?

Q

1. What is their names?

2. What are their names?

It should be 'What ARE their names'. Never 'What is their names.'

This is basic grammar.

FORGET about 1. BAD ENGLISH.

You can say:
What is Fred's LAST name?
(because you certainly know his FIRST name: Fred)

Why do you think that maybe this should be singular and not plural? You have three people. Three names. It's plural. Even though you are only asking about one name for each of them.

Thanks

Q