I have never worked with Google custom fonts but this is how I was able to change Maximenu CK's font family to a usual font like Palatino, Arial or Tahoma:
From Joomla root directory I navigated to modules/mod_maximenuck/themes/blank/css which I assume is the directory containing blank theme's styling files.
Within the css directory, I found the following files: ie7.css, index.html,maximenuhck.php, maximenuhck_rtl.php, maximenuvck.php, moo_maximenuhck.css, moo_maximenuhck_rtl.css and moo_maximenuvck.css.
I was able to change menu font by updating maximenuhck.php
Here is the portion of code to which I added my preferred font family (starts at line 12):
/* menu */
div#<?php echo $id; ?> {
font-size:14px;
line-height:21px;
text-align:left;
}
I hope this is helpful.