You don't need to enable VoLTE. Insert the Jio (VoLTE enabled) in any slot. By default, VoLTE will be active. If it is not, you can change the network preferences from Network option in settings.
Alternatively, you can follow a much easier way:
You can check the below video to get more clarity:
Specs: Xiaomi Redmi Note 5
Yes, Both the sim slots in the device comes with 4G network support across all broadcasting networks in the country. It also provides VoLTE functionality.
To check all the other details of the device through this link Xiaomi Redmi Note 5
I will recommend you Redmi Note 5 Pro. Sporting a 5.99-inch IPS LCD display, it comes with a metal case body and has a thin-bezel design. Under the hood, there is a Qualcomm Snapdragon 636 SoC (8 x 1.8GHz) and it is coupled with a 4GB RAM. With 12 MP + 5 MP Dual Primary Cameras you can capture images of 4,000 x 3,000 pixels. Along with the front camera, an LED flash makes sure that you can make video calls at night. It consists of a 4,000mAh Li-Polymer battery which supports quick charging. It is equipped with a wide range of strong features.
You can also check the complete comparison here: Xiaomi Redmi Note 5 Pro vs Honor 7X vs Honor 9 Lite vs Xiaomi Redmi Note 5