More ghosts appear as you unlock levels. You must have all 5 stages unlocked for Yurei and Conjurer. If you already captured them then turn of Reroll ghost setting in option menu.
Viewing post in Do some ghosts only appear on specific maps?
If you have all stages unlocked see if you have captured them before. Go to the ghost gallery left from where you spawn in the house. Use keypad to cycle between ghost and see if you can see them standing there. If not, they are there go to reroll option in main menu and set it to no. If they are not there then capture other ghost to increase their odds.