Your in a tough spot, but here are my thoughts. Take the path of least resistance. Meet with the builder/gunite company and see if they will rip it out and start over, no cost to you. Remember you signed a contract and did not get what was promised. If they agree, great! If not, don't rush things as this is a huge mistake to correct. You might be out a pool this summer but there are many more to come. If they know you had an engineer out, they might be open to the tear out and redo. You never know, they may meet with you and agree a mistake was made and get to work.
I see a couple of things that could happen if they are not open to the tear out :
They may offer a refund and leave it as and you are left with the project. I don't like this option. You have to think about what it will cost to tear it out and dispose of the material. At this point you may want to contact your insurance. I also hate this path as you may end up with higher insurance cost even though it is not your fault. You could be considered high risk. But if you use insurance, they will be the ones that decide if they want to go after the PB for the costs.
Second option would be to higher an attorney. Talk with your dad if things don't go well at your meeting. I would do this first. Get his advise.
If you have to hire an attorney, remember the more evidence in support of your claim the better. I.E. engineer report, gunite report etc. You need to stack the evidence to make your case. Once again- talk to your dad about that, not sure what the reports would cost, but you may never recoup that money. Not to scare you but I have heard of companies claiming bankruptcy and opening up the next day under a new name. No idea if this actually happens.
In short, meet with the builder and subs if you have to and see if they will correct the problem the right way. If not, my first call would be with your dad.
Try not to get frustrated even though that is near impossible. Be patient, as you want this done correctly. And keep us posted and I hope I see a beautiful pool in the end.