1) I am not sure what are you talking about. It seems that you used the icon element to add the social media icons. As my colleague suggested you need to add a separate section in the Cornerstone and move the icons there and then make the section itself centered. If you want to know more about the sections please read this article:
2) I have another suggestion in this case. I suggest that you clone the same section and make it visible only for mobile and the original one visible only for the desktop. Then you can remove the mtn class for the mobile.
Here is how to hide/show the sections for different device sizes: