By volume I meant that BHs can grow in surface area.

They have neither.
If you mean the event horizon, its area and volume is determined by the mass of the BH.

I have no idea if this evaporation from the center of a BH exits. If it did It would amount to a loss of mass in BHs that aren't eating. I know of no such data

Hawking radiation leads to the evaporation of BHs. I believe that is now well established.