Your father and I were both, however, quite wrong about that.
Or anyway, the pronoun trail is hard to suss out in that portion of chp 53. Who is the speaker in verse 11 who calls the Righteous One “my servant”, and who will allot the Righteous One “a portion with the great” for justifying the many and bearing their iniquities?
There are only two options: the prophet, or God the Father. I think most people would agree (as would I, though perhaps not your father?) that it is God the Father Who allots the Righteous One a portion with the great due to the RO bearing the iniquities of other people’s sins. (Even though, daringly, we might say in utter humility that the Righteous One is our servant. He Himself says so, too, after all, by Gospel report. And He is serving the sinners in his prophecy.)
If this is God the Father speaking, though, then by contextual logic the Righteous One Who has knowledge by which He justifies the many, is the One Who is seeing “it” earlier in the same verse. The poetic construction of the phrase is such that what He is seeing gives Him knowledge by which He is justifying the many through bearing their iniquities. What is He seeing?
Your father (following other interpreters) guesses that the “it” is the anguish or toilsome labor of the Son. (Which the Father is seeing and so is satisfied.) However, in Hebrew there is a pun (or something) in the wording such that what is being seen is light! Or anyway, what is being seen is fundamentally that-which-exists.
The interpretation of verse 11 then would be, “As a result of the toil of his soul, he will see and be satisfied; by his knowledge, the Righteous One My servant will justify the many” etc.
It might even be “as a result of the toil of his soul, he will see and be satisfied by his knowledge; the Righteous One My Servant will justify the many” etc.
Your dad is quite right about there being a distinction of persons in view here; but it is not quite where he (or I for that matter) expected it to be.
This whole section of Isaiah is hugely important, of course. Heck, chapter 54 basically says straight out, or as straight out as you could expect in poetry, that the Makers, Whose name is YHWH of armies, the Redeemer, the Holy One of Israel Who is called the God of the Earth, is calling to Israel like she is a wife forsaken, rejected by her husband (“For a brief moment I forsook you” says her God Who in immediate context is claiming to be her husband), because of the shame of her youth–AND THE REPROACH OF HER WIDOWHOOD!!! She betrays and kills YHWH Almighty and He forsakes her for a moment in some way as a result; not without some wrath on His part either. But His promise is that His wrath will not abide against her forever; and interestingly, He compares her punishment to that of those who died in the flood. Keep in mind, the “swirling depths” of huge bodies of water are a common Jewish metaphor for sheol/hades where even rebel angels themselves are imprisoned until the judgement. The effect is that, when God reminds Israel of His promise to never again destroy the earth by water, He is pointing ahead to a time when (as we still say in naval funerals) the sea shall give up her dead, not to be destroyed again by “the sea”.