Your parents may stay for as much time as they wish up until there authorized stay expires. When a person enters the country on a B2 visa, he/she is authorized to stay for a maximum period of time set by CBP. The maximum stay is typically six months but CBP can authorize a lesser stay. Your parents must leave by the date indicated on their I-94s. You can read more about visitor visas at http://myattorneyusa.com/travel-visas.
Answered on Nov 14th, 2016 at 4:07 AM