Sponsoring GC for Sister and her family

[verabar1]

Hi Everyone, I want to sponsor green card for my sister and her family. She is married and her daughter is 8 year old. My sister,her husband and their daughter all of them have valid Visitor visa for USA. If i file the green card application for them, will that create a problem if they want to visit USA based on their visitor visa ? The family based green card category has a waiting period of 12-15 years and my sister's family will travel to USA during this time, esp. my Brother in Law, as he keeps visiting USA for his office work and assignments. Also what will happen if her daughter is more than 21 years when their green card application is approved ?
Any help on the above questions will be highly appreciated.
Thanks

 

[LucyMO]

it may or may not create problems with entering on a non-immigrant visa. They won't know until they try.

As for aging out daughter - read up on Child status protection act

 

[kittenKat]

Most probably they'll have problems getting visitor visas, because one of the questions on application is whether the petition was filed.

As for age here is a link to the really nice calculator on whether she will pass or not:

http://manila.usembassy.gov/wwwh3228.html