Is there a limit on the number of advance paroles you may apply for?
My parents are green card holders, but still live abroad. While they try and enter the U.S. every 6 months, they have been hassled at the airports on every occasion, for not keeping "continuous" legal residence. I applied for 131 on their behalf, which expires soon. Unfortunately, they have not been able to finish up their business before moving to the U.S. (I think it will take another year or so) - can they apply for another advance parole?
Also, what is the requirement for keeping your green card valid? Is simple entry into the U.S. every 6 months enough, or does it require a more substantial stay?
I'd appreciate any input - thanks!

