Ficus are a Mealybug favorite. You don't mention that you have used horticultural oil. Oil will kill Mealybugs if done correctly. However living in California you probably have a ready source for re-infestation in your yard. So it is likely that you are killing them and they are re-infesting your Ficus almost immediately. You may be able to reduce the number of Mealybug in your yard by introducing Biological controls such as the Mealybug Destroyer, and limiting the use of broad spectrum pesticides, if you use these. The main thing is to stop them re-infesting your plant. If you must after trying everything else you can mix some Imidacloprid into the soil.
Be sure to find a formula registered for house plants and follow the label to the letter.
Another caution on using the Imidacloprid is that it can encourage Spider Mites, so only use it where you absolutely must and watch out for the Mites.

Here is a link that might be useful: Mealybug dispersal

Have you talked with the people at your local office of the Universtity of California Cooperative Extgension Service about what to do? Getting predators in the house to help control them may not be an option and I would not use any broad spectrum poison inside since all of them will cause me breathing difficulties (I cannot even walk by the store displays of the stuff without starting to wheeze and gurgle).
Like scale the best method of control, usually, is a horticultural oil spray.

Here is a link that might be useful: control of mealy bugs