Hello,
My parents came to the US in July 2010 and as per the current return date, they are slated to go back in Jan 2011 (6 months). I wanted to clarify a few Qs regarding changing this:

1) Can their return date be extended by a couple more months?
2) What is the process to do this?
3) What is the implication of doing this on their next trip?
4) Is the 6 months visa restriction per calendar year or is it per trip?

Thanks
Srihari