If you use the supplied 5W charger, it charges to 18 percent in 30 minutes and 35 percent in an hour.
Redmi 6 comes with 5W charger.
Yes, Redmi 6 does have the FM radio 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.