While trying to do this i notice that only first gpu is loaded. Even changing NVIDIA control panel setting didn't help

I found a rather convoluted way to make DAIN windows use 2 or more GPUs:

1. Extract 2 DAIN packages to 2 different folders. Call them DAIN GPU1 and DAIN GPU2 just for your reference.

2. Split the video you wish to process into 2 different videos.

3. Set the environment variable  CUDA_VISIBLE_DEVICES with value 0. For this go to  This PC -> properties -> Advanced System setting -> Environment variables -> System variables

4. Start the first DAIN  (DAIN GPU1) with the first half of the video. It should start processing with the first GPU.

5. Set the value of the CUDA_VISIBLE_DEVICES environment variable to 1. 

6. Start the second DAIN (DAIN GPU 2) with the second half of the video. 

7. You should now have both GPUs working. As fas as I can tell this works for even more GPUs. You just need to keep adding the CUDA_VISIBLE_DEVICES  value and launch more DAIN instances.

8.  Join both resulting videos with a video editing app of your choice.

I hope this helps.