adoption of sister\'s child will keep you in India for 2 years.
if the child is not an "international Orphan" ( defined in a rigorous and narrow way !), you will need to demonstrate that, prior to the child reaching age 16 years, 1) a 2 year period where you had legally ordained PHYSICAL Custody, excercising day-to-day care of the child and 2) complete, finalized legal custody, (adoption decree). There are no waivers available. Check several of the US Embassy\'s websites, including the ones in China and Guatemala for more information.