will it be legal to stay after B2 expired? I130 and I-485 are filed concurrently, but might not receive the receipts before B2 visa expired.

Your father is currently in a state of grace with U.S.C.I.S. in the sense that he is technically not illegal after his B-2 stay expires. However, he is quasi legal during the time that his I-485 application is pending. immigration will not bother him during the time until a decision is made on the I-485, but he is best advised to stay away from the border regions. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.