To get rid of bone piles, I usually just rush them holding a shield to block arrows and using a club or mace. Get that thing upgraded and it 1-2 shots most skeletons. Clear the area then smash the bone pile. Stagbreaker can also break them through doors depending on spacing. Arrows and fire arrows are pretty useless against skeles and their spawners.

Edit. Its not a bad idea to take your time when dealing with spawners, good way to level combat skills.