I'm contracting out the foundation and framing, but the rest is all me. I'm not keen on the severe upcharge that builders add. But i'm also a glutton for punishment
If the foundation doesn't match the plans, it's a severe issue. Your son can contact the building inspector to let them know that what's currently being built does not match the plans. New plans would have to be drawn up, approved by an engineer and then accepted by the town. Now I believe that randaccio uses subs for almost everything so either a wrong drawing was relayed or the sub just screwed up completely.
I was just walking by a couple of the new builds by randaccio in Windsor Ridge South. I wasn't a fan of the foundation and basement beam layout on one of them. Looked under-engineered to me.