Hi there!

I played Divinity: Original Sin for a while via steam family sharing and I want to buy I now.
Are the steam saves compatible with the GOG edition? As I don't want to start over.

Thanks!

//Acenoid

Yes. Install the game and patch, and you'll be able to continue with your existing saves.

In general there could be issues when Steam is updated until the GOG version is patched, but that is not the case here (both are currently at 1.0.81).