I owe $4k (I don't know how it got that high) to citicard and they harass me about it call and hang up. I think they sent it to a lawyers office, I have no income at the moment. Can they sue me if I don't have any income. I have a wife and two kids, the only person working is my wife and we can barely get by monthly

Sure they can. It makes it harder to collect, but they will try to get a judgement on the chance you start earning money.