Visitor Visa Extension advise..

[mitreta]

I am US citizen My parent are here in visitor visa and they have 6 month stamp to stay but they want to stay for another 6 months so total time 1 year and then they want to go back to india for 3 to 4 month and then they want to come back to US and apply for green card is it advisable to extent another 6 month visa or no or it will give problem when we apply for Green card. Pleas Advise .

[kabkaba]

Visitors are generally expected to only visit and not stay. Your parents can file I-539 to extend their status before their I-94's expire and if USCIS feels that they have a genuine reason it may get approved, but generally it is difficult to prove genuine reason.
If it gets denied after their I-94's have expired, their Visas are automatically void and their illegal stay is counted from their I-94 date.
Even if it is approved, they may need to spend more time abroad before they can return in Visitor status.

If you are planning to file immigrant petition anyway, it is better if they return according to their I-94 now and return after 8-9 months or so.

Also, don't post your personal email id on public forums. Anybody in the world can see it.