This game is also available on Xbox 360.
Familiars increase mainly by number of kills rather than experience value, especially with Alucard at very high levels. Exceptions are made for Bosses (higher) and Blood Skeletons (none). Find a location where lots of enemies constantly replenish, such as in the Marble Gallery in the inverted castle, where Medusa Heads appear, or in the reverse Caverns, where large numbers of Dark Octopi can be found. Equip a fast weapon, choose your familiar, and start slashing.
Once you have a duplicator it is extremely easy to level up the familiars. Go to the reverse caverns in the area after fighting Doppleganger 40. In this area is a room with lots of Dark Octopuses. Drop down into the room and use a Bat Pentagram then a normal Pentagram and jump back out. Each time you do this, you will get 20 to 30 experience for the familiar, and it can be done many times in one minute.