Which are the best dual sim 4G phones with VoLTE available in India?

You mentioned the best so I will have to say its Oneplus 3T & Samsung Galaxy s7 / s7 edge.

And if you are searching for the best smartphone in low price range then go for MI Redmi note 4.

Oneplus 3T Key specs:

Price: Rs.29,999

Screen Size 5.50-inch

Resolution 1080x1920 pixels

Storage 64GB

Processor 1.6GHz quad-core

RAM 6GB

Rear Camera 16-megapixel

Front Camera 16-megapixel

OS Android 6.0.1

Battery Capacity 3400mAh

Processor make Qualcomm Snapdragon 821

DUAL SIM WITH VOLTE.

Samsung Galaxy S7 Key specs:

Price: Rs 43,400

Screen Size 5.10-inch

Resolution 1440x2560 pixels

Storage 32GB (With Hybrid Memory Card slot)

Processor 1.6GHz octa-core

RAM 4GB

Rear Camera 12-megapixel

Front Camera 5-megapixel

OS Android 7.0

Battery Capacity 3000mAh

Volte with hybrid sim slot.

MI redmi note 4 Key specs:

Price : Depends on how much ram you want

Screen Size 5.50-inch

Resolution 1080x1920 pixels

Storage 64GB

Processor 2GHz octa-core

RAM 4GB

Rear Camera 13-megapixel

Front Camera 5-megapixel

OS Android 6.0

Battery Capacity 4100mAh

Volte with hybrid sim slot.