I have found that on my level 14 sniper and sorc both can activate 2 abilities at a time. So il start casting snipe and then push the regular shoot attack and itll shoot both. Same on sorc exept it's the lightining one. My question is: does this work for all abilities? And also do both of the abilities do dmg when hitting?

What you are seeing is the one ability getting used when the cast ends and then the instant ability getting used immediately after. Casted abilities are not on the global cool down since they have a cast time, but after your auto attack (or any instant attack), you wouldn't be able to use an ability or start a new cast until the 1.5 second GCD has elapsed.