B2 visa parents query

My parents were in US on B2-status and there I-94 expired, We had filed extension application 45 days before I-94 expired.we have receipt notice and 13-digit case number by Uscis which is proof of existing I-539 document in process. But the application was filed for 3 month extension which will be ending on May 1st… Given the current situation in India, we want our parents to stay 3 more months here.Is it legal to stay for the whole 6 months as we filed I-539, even though the application was filed for 3 months? Please advise

We strongly suggest to file another extension before your current requested term expires.