You can record up to 1080p resolution videos with Redmi 6.
No. Redmi 6 does have a dedicated MicroSD card slot and 2 other slots for SIM cards.
Yes, Redmi 6 does have GPS support.
Yes, Redmi 6 does have the dual apps support. You can have 2 WhatsApp and 2 Facebook accounts at the same time.
If your budget absolutely can’t exceed the Rs. 8,000 mark, go with the Redmi 6 without any concerns whatsoever.