>>7 Dream catchers are made catch nightmares, not ghosts.
If you want to go the religious route: Get a priest's blessing, put a line of holy water at all entrances of the house, and put an iron or tin cross in the most heavily affected areas.
If you want to go the spiritualist route: Walk along the perimeter of every room while burning dried sage, put a thick line of sea salt or rock salt at every entrance, and burn incense in the most heavily affected areas (this will also help get the pot smell out since sage smells really bad and your parents might misunderstand).
I'm not gonna comment on the OP since you seem to know what you want to do; I was just extending off what Xenon said
>>7.