Thinking about adding a couple Mics to my cameras but it's too late to run 12v now. Are there splitters that allows me to power both the camera while giving a 12v output on a single cable?
Yes. You can get a PoE splitter to 12v and ethernet. Add a Y splitter to the 12v end and power the 12v connector on the cam with one and the mic with the other. Easy peasy. Same "trick" works with lower powered external IR illuminators.
He ^ is also right. I have a gizmo like that. Doubles your effective power over a single ethernet cable. Full PoE for one camera and another for one or more accessories. Also very handy for doubling connectivity over a single pre-existing run.