Why did you give up on using EXR (https://blender.stackexchange.com/questions/174098/i-have-tried-to-import-exr-files-to-davinci-resolve-with-the-luts) and go to a useless format like PNG?
PNG cannot handle unassociated alpha channel, it cannot have pixels that are emissive and transparent at the same time.

Go back to EXRs and be happy.

As for the glow on other elements you have two choices: Create some geometry in blender that will be affected by the fire and use it to add luminance to the scene in the compositor of your choice (fusion can do that) or even as a track over the original footage in davinci. Or use masks on the footage and selective color correction and try to recreate the effect on other elements of the scene.