The download zip from the themeforest has a zip file named extinct-child.zip which you can upload just like you upload any other WordPress theme in the WordPress admin dashboard. When you extract the download zip, you should find this one. Else, let me know and I can send it across to you. Using a child theme requires some knowledge of programming and if you have already made the changes to the parent file, I would ask you to not worry about reapplying them here in the child for now. If you have any custom CSS that you have defined, you can move them to the style.css file of the child theme.
I still need to check your site on my mobile. Will have a look and get back to you. Must be browser/OS specific issue that is making it difficult to handle the long URL or Facebook itself is having a problem redirecting to mobile site of theirs from this URL. That is my best guess at least.
About changing the colors, the PSD files are already part of the download bundle and we just posted the image files for that user; images which were created out of the PSDs. They will probably not meet your need since you would have your own custom color. If you still need them, let me know and I can send them across to you.