Not seeing the age of the packs, my routine would be to grown up one pack in the starter and then pitch with the other two packs. If you overcrowd the starter with too many cells to start with, they will not multiply. Any recommendation really depends up on the specifics of the recipe, the viability of the yeast packages, and the number of cells you need.
Just off the top: you need somewhere in the vicinity of 440 billion cells. If you packets are one month old, your viability would leave you with around 77 billion cells in each packet.
A 1.74 liter starter on one of the packets would give you approximately 330 Billion cells. Add the other two packets and you would be pitching 484 billion cells.
There are a lot of assumptions in the above calculation, but you can just plug the numbers in and check based upon your actual information.