The brew easy is essentially a full volume mash, BIAB process with the only difference being the total volume of mash is split between two vessels. The profile in all software you would use are built around BIAB and no sparge. The water calculations, including salts, acids and volumes should just be based on the total water.
In my opinion, the dough in phase should begin with pumping almost all the water up into the mash tun (make sure you disable the BK element first) or as much as you can fit along with the grain. Keep in mind that grain displaces .075 gallons per pound so 10 pounds needs .75 gallons of space. Stir the grain in gently and let it settle for 10 minutes. Then allow at least 4 gallons of wort to drain to the boil kettle, set the autosparge float at that point and begin slow recirculation.
The alternate way to do it is to keep all the water in the boil kettle, put all the dry grain into the mash tun, then pump all but 4 gallons into the mash tun through the drain port to underlet the mash.