If II followed the schematic the boiler two fires and a Arger would be supplied by a 22mm gas supply.
I'd suggest you do a quick estimate of the size of the gas pipe and submit a written query, keeping a copy. I'd also keep a copy of the schematic and check any specification for any clauses requiring you to check pipework sizes. Keep a copy of the schematic, because they'll be looking for someone to blame if they've cocked it up.
You still can't install the cylinders without the 2-port valves, regardless of what their schematic says, there must be something to control the cylinder temperature.