My parents has green card and they are in India for last 10 months. We did not file reentry so they will loose Green card after one year. They don't have any plan to return US So we decided to give up (surrender) green card and at the same time apply for 10 year multiple visa. My question is what's difference between B1 and B2? What's form I need to fill up for 10 year multiple visa? Since they already had green card. Do they still need sponsor for multiple entry visa?