j2签证多次去美国？
1.J-2 visa is a kind of student visa for the F and M status students， as well as their dependents： spouse(F or J) and children (child under 21 years old if unmarried; other child if minor ) This visa can be applied to multiple times because it is not limited by number of entries. However， you should keep a valid reason when leaving/entering US every time： your job needs you back in US etc... If you do something without permission like overstaying， there will be a record on your passport that may affect your future application. So just follow regulations carefully！ As far as I know， most of Chinese students go back to China after graduation（at least they are my friends） so chances are low that you need apply this again and again．
2. About green card， according to what you said above， your parents cannot directly get green cards through you since they’re only your dependants with no working permit. One way is to wait until one day you have full working rights and then sponsor them yourself， which means they could live with you legally here all the days but probably won't have right to work； also another way is waiting till both of you become citizens， and once you acquire citizenship， your parent would automatically come into lawful permanent resident status too～ The process takes around ten years from applying citizenship to getting result.
3. Well， maybe some companies allow foreign employees get H1B even he is married. But usually an employer has to pay lots of money each year to hire those workers， and such expenses might increase company's overhead cost hence decrease profitability． For example IBM used to use its own engineers who earned at very high salary level instead of hiring H1B workers whose wages were often cheaper than American ones， because it was more economic for these big corporations to train local talents while paying taxes. Nowadays they still choose native Americans rather than foreigners due to strict policy made by government， although they say they respect diversity and internationalization！ In fact many Fortune 500 companies don't hire foreign employees except when absolutely necessary， e.g. IT related jobs. And Google had hired quite few H1