apply for tourist visa, once they get it, they can travel for 5 years. goodluck.

you can petition for them in USCIS. but you should have sufficient source of income to support them so that they are not gonna be public charge.

........but your parents get a position in queue (line) for immigrant visa, once they reach in their turn, they can attain interview...................if they are eligible and visa number is remaining they gonna get diversity visa (green card)

or you can go as SAJHAFAN to apply for tourist visa.

goodluck