Visit to U.S.A while family based greencard is in process

[sanjay.sinha84]

My US citizen sister is going to file for my father and mother's greencard under the family based greencard category in December 2021.Both my father and mother are citizens of India and they both have valid U.S visitor visas valid until June 2027.In this case, can they visit my sister in U.S.A in March 2022 while their family-based greencard petition filed by my sister is still in process?If they can visit U.S.A while their greencard petition is in process, and lets say if my parents receive the good news of their greencard approval while in U.S.A and they apply for adjustment of status, can they visit me in Canada while their petition is still in process? I am a Canadian permanent resident living in province of British Columbia in Canada, thanks.