About Gale - use magic missile. It's a spell that can't miss, and you can use it to hit multiple targets for small damage or one target for bigger damage.
About Wyll - I wouldn't use him anywhere near the front lines. Wyll needs to spam Eldrich Blast from some place high. In level 3 (I think) he gets teleportation spell. Use it to put him in a spot when he can rain hell.
Astarion - aside from being a little squishy he is very good. I found that it's best to equip him with two weapons.
About your ranger I don't know much, since I didn't really played ranged ranger yet (strangely the ranger right now has a lot of potential as melee fighter for some strange reason). I would say to take horde breaker either way, as it allows you to attack twice per turn if the enemies are close enough to each other.
