Thanks for all the imput! In fact my dad has had many tourist visas before, but last time he was here was in 1990.... a lot changed since then. At the POE they will probably give them 6 months but in reality they will only stay here for 1 week because they have to go back to work, my brother has to go back to school, etc... But they were planning on coming back for the holidays, they are are just frustrated bc they'd have to apply again!
Another interesting thing is that there is an annotation on their visa saying: "Daughter's wedding in Ohio" So at this point I think if it weren't for me providing documentation to prove we have a hall and catering all paid for, the consul would end up denying their visa.
Now after I become a citizen, I have no plans on applying for a green card for them because having a green card is high maintenance, they wouldn't come here often enough to maintain it. Do you guys think that it's okay for them to get a B2 visa once I am a citizen?