Please, I need help.

1is correct, 2 is correct 3 ability is good enough to be able to do that work.4 that are able.

Thank you.

(in reference to #4)
People are not impersonal objects, so we should avoid using "that" for "who."

How many people are there to do that kind of work?

That refers to work, not people.

No it doesn't. Since you didn't bother to check what I was referring to, I won't explain why it doesn't. I don't put up with Netwits who jump at Gotchas without thinking.

But you have professional company. Recently a yakker in the media said that Romney getting the 64 electoral votes from the Rust Belt wouldn't make a difference because he lost by 126 votes to Obama. This professional, whom we are told to look up to because of his position, was so stupid he couldn't figure out that what was added to Romney would have been subtracted from Obama, doubling its value.

Your sentences in all were ok. But telling that guy off was even greater (No it doesn't. Since you didn't bother to check what I was referring to, I won't explain why it doesn't. I don't put up with Netwits who jump at Gotchas without thinking.)