Is the car actually a total loss? In other words, do the repair costs exceed the market value? If they do not, your son can insist on it being repaired (ignore anything your insurer says contrary to this, the contract of indemnity is one by which the promise to indemnify your son up to the market value). Definitely request a copy of the assessor's report and do not let the insurer control your asset. If you have the facility to store the vehicle at home, I would do so. Once that vehicle goes to salvage, it is very very common for them to get further damage and very hard to get them back.
The value should take into consideration the optional extras if the vehicle is a total loss, but you may find that Glass Evaluator and CAP motor research do not take them into consideration. Insist they are added to the value. A good engineer should do this by applying the same rate of depreciation the car has sustained and applying it to the value of the options new. Make sure the insurer's engineer does this, as they never, or very very rarely do.