B2 Visa Extension For My Parents

[Nash07]

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My parents have 10 years visa. They visited us last year and stayed here for 6 months.
They again entered US on Jan15th of this year. But this time they have got
I94 just for 3 months, upto Apr 14th. They are in California now. They have to visit my brother who is in Chicago and Me in Dallas.
1. What best reason can we give to get the extension? My brother has purchased a new house. So they have to visit him. Is it a best reason?
We have some personal issues also for which they have to be here. Please suggest.

2. Their port of entry was San Fransisco where they are now. But they were sponsed by my brother who is in Chicago. So in which center should they apply for the extension?

3. Also let me know how sooner can we apply for the extension(Can we apply during 1-2nd week of FEB as the I94 is expiring in Apr)
Can they stay here till they get response from the USCIS even after their I94 expiration? R there any problems if they do so?

Please let us know.
I will be waiting for your reply .

[immihelp]

I suggest you read https://www.immihelp.com/visa-stamp-...ration-in-usa/ completely before applying for visa extension, particularly the last section.