I've been looking for games that I can play Co-op with my younger brother while we're both at separate colleges and think Divinity would be a good one. However, we share a GoG account, and before buying it, I"m curious as to if we could play together with just one copy, or if 2 different copies are necessary

You each need a copy of the game; the same is likely true for the other games you are 'sharing' and for the GOG account.

The Enhanced Edition (to be released later this year) will include a dynamic split screen mode for local co-op, but you would still need two copies for online or LAN multiplayer.

Ok, thank you. We'd been playing games like magika and portal 2 split screen over the summer, and I was checking to see if Divinity needed 2 separate copies. Haven't had much experience trying to work over the net yet, which is why I didn't know and asked. Thank you for your help

It's also against the rules to share a GoG account. If you purchase a game on GoG you purchase it per household. You are not allowed to install it on any location other than the one you purchased it for.
So even if it technically worked, you will still need to purcase two copies of each game.

Can you (or Larian) clarify this? The way you state things I would only need to purchase DOS once and could then play coop by installing it on both my wife's and my own laptops - one household purchase. I've actually been super lazy about getting DOS, but I'm this one answer away from backing DOS2.

Btw I'm not trying to cheat or breach anything, I'd just like to save a buck if I don't need to buy multiple copies for everyone in my house.

Technically / legally you need to buy separate copies of the game to play co-op on different computers.

The Enhanced Edition of the game will support local co-op (ie on the same computer), with a dynamic split screen, when playing with 2 controllers. Target for release is late October.

One of the D:OS 2 tiers includes a copy of D:OS EE (GOG or Steam key), and it might become available as an add-on, or possibly in other tiers that may be added.

Cool, thanks. was eyeballing the D:OS Pack tier. Do you think you'll be adding add-ons to the Kickstarter? like adding additional copies and stuff?

Yes, and possibly additional tiers.