Yes, you can use the 4G Jio sim card in Comio C2.
Comio C2 comes with big 4000 mAh battery. It offers talk time of up to 20 hours and standby period of about 500 hours.
Yes, Comio C2 does have the front camera flash.
Yes, you can use 2 4G sim cards in Comio C2. But at any given time only one sim card will work on 4G network.