Ab12,
I am not cutting you intention to help people. But here some things else is happening other that seeing the spirits.
Yes you are true, if some one built a house in the graveyard they may see the spirits around their house. In that case if you just light a diya and agarbathies in the evening that may keep this spirit away from that house. But if some has send these spirit intentionally to hurt of to damage that house, just doing japas may not work. I n this circumstances you may need to take help from a pandit.Gurji/Jyothishi to help. But beware of false pandit.Gurji/Jyothishis