1. He does NOT need a 3" vent at each toilet, and if he used 2" he would not have to reduce it in the attic
2. In most jurisdictions, the total AREA, of the vents through the roof has to equal the AREA of the incoming sewer, meaning that a 4" sewer line would need FOUR 2" vents or some combination which was equal to at least 12.56 sq. in. If he does not know this, then I question the "impeccable" part of your statement.