These are actually some of the best people to have looking at your work. Otherwriters are great, and they can really help with technical stuff, but general audiences that'll be reading your comic are more than likely not writers. Pretty much all of the people I have doing our read through on rough scripts aren't writers by trade at all.
If your friends are distant and busy, schedule a skype call once you have the draft finished. More than once I've done a read through that way too. Ask them to help and offer a day in the future you can all agree to chat on. Then narrow it down to time.
From there it's all about making sure that they know WHAT you're looking for. I usually tell my folks, "Okay, if something jumps out at you as confusing, or nags at you, doesn't make sense or has a grammatical error (outside of obvious accents etc), mark it and lets talk through."
Big plot holes will show up. Text you've written will be hella cliche in some parts. In fact it MAY suck and that's perfectly okay. The first part of getting something good is finding it's flaws. If you find a lot of them, just think how much BETTER the next script will be!
But first...you need your script. <3
Good luck, bb!