If you want to achieve two mated queens I would suggest you start with at least 6 cells. From them select the four best, and make up four nucs.
From them with luck you will get at least two mated queens, and on you go.
However possibly this is where an investment in say four mini nucs would come in handy? Because you reduce your expense in bees to four mug fulls. Lot less costly than 8 frames of brood and bees. Remember when you make up a two frame nuc you do not just put in the bees on the frames you are adding in but at good shake of bees from at least another frame... adds up so it does...
PH