who is/are

You could use either "is" or "are" in the first sentence. In one case, "is" agrees in number with "who," which is singular or plural depending upon context. As that sentence precedes the sentence in which "them" appears, the pronoun "who" could be taken to be singular, and "is" would be correct. If the second sentence preceded the first, it might be considered correct to use "who are"--but it might still sound odd to the ear of a native speaker.

Let's switch them and see.

"If Najib as prime minister choose them as ministers, his political party will lose the next general elections. People are watching and we know who is corrupt," he said.

I don't think it matters, Set, which sentence comes first. There's nothing that would prevent a speaker from thinking of these people in an individual sense or a collective sense.

Off the top of my head, I'd say that 'is' may be the more common but, overall, I agree with you. I don't see any problem with 'are'.

"If Najib as prime minister choose them as ministers, his political party will lose the next general elections. People are watching and we know who are corrupt," he said.

Thanks, Setanta and JTT.