There are certain minimum punishments that go along with DUI's in Pennsylvania depending on the BAC level. A graph from the Pennsylvania Commission on Sentencing with those required punishments can be found here
Whether or not a reduced sentence
can be achieved depends on the defense lawyer's negotiation skills, the disposition of the district attorney (I can almost guarantee what will happen where I practice once I find out who the DA is on the case), and the judge it would end up in front of.
That said, it does appear this attorney has an issue with professionalism. I understand why that would certainly be disconcerting.
You have the right to fire him for the second case and demand a return of the retainer. If he does not comply, you would then have the right to make a complaint
with the state bar and open a fee dispute.
As you and your son are uncomfortable with his representation, I would recommend that you find someone else you do believe is doing his best for you. At the very least, consult with another attorney and have him evaluate the result from the 1st DUI. If he feels he can do better, your son may be able to withdraw the plea if the court permits.
If you have more questions please feel free to ask. I'll be happy to answer them. If you do not, please do remember to rate my service in assistance to you today.