Probably the simplest way is to use Multi-View cameras as described in this answer. All that is required is to enable ‘Views’ in the Render Layer properties and configure one view per camera with a particular suffix. Set your cameras with the same name and matching suffixes - so, for example, you could have suffixes of ‘_L’, ‘_R’ and ‘_T’ for left, right and top, and name your cameras Camera_L, Camera_R and Camera_T.
When rendering you will now get an image produced for each view. Each inage file produced will bear the relevant suffix - eg, ‘0000_L.png’, ‘0000_R.png’, etc.