Not sure with insta dng's but I've had some success with ricoh Theta and photoshop.
Import DNGfile, crop to the left fisheye half extent and save as jpg, then import again and crop to the right half to save as new jpg
just make sure the left and right cameras are always exported into different folders and you let Metashape know they are different cameras. Use the photos as multicamera or as single camera files, its up to you.
Regards
José MartÃnez
Geobit & Accupixel CTO
Metashape training providers