Replacing older Leviton dimmer with new Lutron different wiring
The black wire from romex 2 is the hot wire that feeds your three switches and is the common. Remove the red wire from switch 2 from that bundle and hook up the black wire from your new switch to that bundle. Then take the two black wires from your old switch and hook them up to the red wire and the red/white wire from the new dimmer. All your new switches need to be hook up to the ground wire.