The first time you crossed the broken bridge heading to the stair set that leads to the front of Ingward's Ghost House there was a fog wall you crossed. That is a ghost leash point.
Go to the front of the house near the door and look down to the lower left--away from the front door-- there are three ghosts outside the 4 Kings tower that are already heading up to you. When they are about 50 feet from you slowly retreat to the stairs. Don't go more than 1/4 up the stairs and the three should come into attack range. If you head half way up the stairs the farthest one will leash and you should still have two, which you can easily kill.
About this time one or two ghosts should be coming through the wall of the ghost house to the stairs. These won't leash until you run back up to where the fog gate was. But should only come as a two pack.
After dispatching the first four, go outside the front door and lure that lone remaining ghost in the water below you near the 4 Kings tower and kill it. If you don't retreat to the stairs another two to three ghosts will come out of the walls near the door to the ghost house.
Once you clear the few ghosts from that you can step inside the house, but do not go farther than that entry room. Stand there, run a circle, smash a pot and you should draw the attention of four to five ghosts in the fireplace room and the two hallways one either side of that room. If you need, retreat to the door and outside. Most will leash before you even get to the stairs.
After you kill about five in that entry hall check the two hallways and make sure they are clear. By check I mean move just inside the hall and wait to see if a ghost ascends or depends on you.
The ghost house has a basement level that ghosts come up from and some hang up near the ceiling inside the house so expect them from all angles.
Once both halls are clear you can step inside the fireplace room with the ladder to Ingward. There is a single female ghost--the females scream when aggroed-- that you can quickly take care of before the final two ghosts come down through the walls from the upper chimney.
Those should be the last three ghosts you have to deal with and can safely explore the area, including Ingwards roof.
Praise the Sun!