The contestants in the quiz show sat wth we,us audience members.

I think us because it is an object?

For we, us scientist, the discovery of a new planet would be exciting.

I think us?

In the sentence, "The contestants in the quiz show sat with we, us audience members," the correct pronoun to use is "us." To determine which pronoun is correct, you can try removing "we" or "us" from the sentence and see which one sounds more natural.

For example, if we remove "us" from the sentence, it would read: "The contestants in the quiz show sat with we audience members." This doesn't sound quite right, as we don't typically say "we audience members."

On the other hand, if we remove "we" from the sentence, it would read: "The contestants in the quiz show sat with us audience members." This sounds much more natural and is the correct form to use.

Similarly, in the sentence, "For we, us scientists, the discovery of a new planet would be exciting," the correct pronoun to use is also "us." By removing "we" or "us" from the sentence, you can determine which one is appropriate.

If we remove "us" from the sentence, it would read: "For we scientists, the discovery of a new planet would be exciting." Again, this doesn't sound quite right.

However, if we remove "we" from the sentence, it would read: "For us scientists, the discovery of a new planet would be exciting." This is the correct form to use as it sounds natural and grammatically correct.

You are right for both.

How about these...

The ones who defeated the scary monster were Gerry and them/they.

I think they because it is a predicate pronoun,

The ballerinas featured in the show were Bernice and she/her.

I think she due to a predicate pronoun?

Yes. Both are correct.