in 1-4 or 1-5... when you are going for it get: a lot of most damaging arrows you can get, and every item that lets you carry more stuff. If you are playing heavily armored character its better to let npc die(get his items asap otherwise they will dissapear).
Oh, and don't go into 3.. just don't. Do it only after you get strong weapon(Meat Cleaver or better) and character because if those guys there hit you with spell once you are as good as dead(and sometimes your souls will end in weird place) even with dark silver(100% magic ress) shield.
After clearing 2-3 go to 4-1 and finish it - boss is easy but you have to get down to him ASAP. Hit him where it will hurt him the most. Watch out for red eyed black skeletons and golden skeletons. Golden ones are problem - because they hit heavily, knock you back, and you have to fight them on tight ledge. Avoid black ones or kite them - don't even try, or better don't even thing about, blocking - they will just slice you apart. Your best bet is to: avoid them, or kite them - they will follow you for a while but when they turn back you can just stab them(use heavy-hitting weapon or something with multiplier to critical dmg) - do it only on soul form and with ring that helps you sneak.