You can certainly rig up two ammeters. The simplest method is to use ammeters with a current clamp- just fit one to the positive cable of each battery and it will show current flowing in or out of each. No need to cut into the existing cables.
You can connect a voltmeter to each battery too, though when they're connected in parallel the voltages will be equal, and it's best not to have them permanently connected.The voltmeter for the starting battery can be switched through the ignition. For the auxiliary battery I'd power that via a relay which is controlled by the ignition switch.
For gauges, I think the ideal would be a dual needle gauge if such a thing exists- either a combined voltmeter/ammeter for each battery, or a dual voltmeter and dual ammeter- this would save having four separate gauges. Not aware of any specific products though.