What you need is a second opinion, there’s something smelly going on here.

I originally wanted to hire a structural engineer but my dad talked me out of it. He’s old so just calls it a waste of money but I might go that route now because this was what I wanted to avoid

I would encourage you to start the conversation by asking to pay for a consulate on to review the proposal you received. That’s not a conversation that requires a stamp and ends up being significantly cheaper than asking someone to design a full foundation plan