I would forget the dragon for now in terms of killing it, it would take a while to shoot at it and melee would probably get you killed. If you can lure it down and run by it to open the gate, that's very useful though.
The boar you can just run past down the underground path on the right, or get inventive - you can backstab it, you can drop on it (like the asylum demon and taurus demon), you can lure it in to the fires around that area and it will kill itself. You can use the alluring skulls you find in the area to do this. That's kind of how the game rolls, pay attention to environmental clues to help you.
Just take on the hollows one at a time, don't run ahead and have a load of enemies chasing you. You're so close to some very useful stuff just a little past the boar!