I currently have a Carbon 12 at the console and Carbon 9 at the bow that are networked. I'd like to add another 12" at the console just to run mapping, does anyone know what models are compatible that will allow all 3 to be network together to allow waypoint sharing?

I believe HDS units (gen 2 and newer), Carbons, elite TI’s, and live units will all work. I don’t think the Hook’s will network the way you want

the elite tis have to be networked from a nema 2000

Technically all the HDS models will link, but only gen3 + will link to a carbon without forcing the carbon into 'legacy mode'. This will force the carbon to act like a gen 2 from what I was able to figure out when I was researching the exact same question. The TI models will link mapping only through a nema network, but they don't have ethernet. And waypoints will only share on that nema when both units are on. And I think its only like you can see the waypoint on the map but it doesn't actually transfer and save to that unit. With all that confusing stuff, you really need a gen 3, carbon or live unit to do it right.