I am writing a video mixer patch with 2 videos using the pix mix object but I can't get the audio to work and I'm not sure how to do it. Any help would be great.

you need to be more specific with some details here...
are you trying to play the video included in the video files? if so i'm not sure what approach you'd take, it seems all the [pix_***] objects related to video are just that, only video... maybe rip the audio off the video and use the same lookup control on the array with the audio that you use to read through the video, so they stay in sync...
you can never include too much info when looking for help, your post is a bit vague to respond to in detail... i don't know pdp much at all but maybe there's an alternative there (and i know there's objects like pix2pdp and vice versa if i'm not mistaken, so you can mix pdp and GEM where you'd need to)...
also always make sure to patch to a DAC~, check the test audio and midi screen in your menu, etc... on multiple occasions i'd pull my hair out wondering why something wouldn't work only to realize the instance of Pd i was running didn't have 'control' of the soundcard and therefore wouldn't output any audio.