I'm a bit confused as to what I would use for this sentence:

The first in line at the theater were ____

Would it be "them" or "us"?

Along with:
Karina and ___ are working together to build the model.

1) her
2) me
3) she
4) us

If you could explain to me what it would be instead of give the answer, it would be REALLY helpful. Thank you!

Getting a little hostile, no?

Was just saying how the answer was given to me; wasn't denying your knowledge.

However, you did help! :)
Thank you, have a nice evening (or night!)

So the first sentence, instead of "us" or "them" would rather be "she and him"?

Also, that means the second is correct?

For the first one it doesn't really give an exact subject pronoun that stands by itself. If I were to choose "she" it would have to be paired with "she and him"

Haha forgot to say which one was the second! woops!! :)

The second I'm pretty sure is "Karina and she" however that sounds awkward to "Karina and her."

She is a subject pronoun. But you wouldn't say "Him is first in line . . ."

What is your answer for the second one.

It's awkward, but in both sentences, the pronoun should be a subject pronoun. The first is a predicate nominative. The second is a subject.

http://www.grammar.cl/english/subject-pronouns.htm

No, not "she and him!" Him is not a subject pronoun.

Katrina and she is correct.

I know some of these constructions seem awkward because many people misuse them.

When I get a phone call and someone asks, "Is this Sue?" I always answer, "Yes, this is she!"

You're welcome. :-)