Hey JEREMY,
I am really sorry that delay of this reply,
I've checked in your site, it seems like you missing enable display these custom field in your mini registration from backend > Easysocial > profile type > Registered profile > custom field tab > e.g. edit `username` field > click view tab > Appear in Mini Registration - YES
By the way, I already help you enabled it, these custom fields should be appear now.
hope this help.