Yes, Xioami Poco F1 supports VoLTE in both the SIM slots since VoLTE works on bands 3,5 and 40 and both the SIM slots in Xiaomi Poco F1 supports band 3 and 40. You can use two Jio SIMs at a time in Xiaomi Poco F1.
You can go to this link for complete specs: Xiaomi Poco F1
Yes, POCOPHONE F1 support 4K video recording. Ultra High Definition or 4K possess 3840 x 2160 pixels, which are 4 times as many in Full HD or 1080p.
This massive increase in the number of pixels enables you to capture extra fine details with the following benefits:
You can find complete specifications here: POCOPHONE F1