Add new editors (by other editors)

HI! I have added one additional editor to my project, so we are two now and i have paid a year for two seats. But today additional 15usd was charged for another one seat. I did not invited this third editor by myself. Is it possible that my second editor has a permission to add someone else? I thought only me as an admin can do that. Can i as an admin invite only people that i approved and demerm this permission for other editors?