Okay, let’s start this off by acknowledging that no one is actually untouchable. If the Angels called the Dodgers today and said “We’ll give you Mike Trout and Shohei Ohtani and we’ll pay their salaries, all we want in return is one prospect named …,” Andrew Friedman would have the paperwork written up before Perry Minasian had even said the name of the prospect.
With that said, there are a few prospects in the Los Angeles farm system who are essentially untouchable, meaning there are no realistic scenarios in which the Dodgers would trade them, for a variety of reasons.