“This interpretation leads to a reading of πάντες ἥμαρτον (“all sinned”) that is itself improbable. In the Augustinian interpretation, this refers to the whole human race sinning in Adam in a collective and participatory way. As Augustine himself puts it, “all have broken God’s covenant in that one man in whom all sinned.” The idea is that Paul speaks of an involuntary participation in Adam’s sin by an actual participation in Adam’s nature. Adam is not simply an individual, but the primal instantiation of human nature, and so the consequences of his fall not only affect him personally but also affect all his descendants subsequently and distributively.47 In our estimation, the theological underpinnings of this view are not in themselves objectionable; indeed, one can find precedent in Scripture for such a manner of thinking (see Heb 7:6–10). Nevertheless, the fact remains that, in his letters, Paul consistently uses the verb ἁμαρτάνω (“to sin”) for actual sins committed by morally responsible persons in the course of their individual lives. That he has this default meaning in mind in Romans 5:12d is nearly certain: earlier in the letter he uses the identical Greek expression to insist that “all have sinned [πάντες ἥμαρτον] and fall short of the glory of God” (Rom 3:23)—an unmistakable reference to the universal occurrence of actual sins—and two verses later, in a passage intended to preempt objections to 5:12, Paul speaks of multiple generations of “those whose sins [τοὺς … ἁμαρτήσαντας] were not like the transgression of Adam” (5:14). For these reasons, the translation “in whom” falters on linguistic grounds.”
Hahn, S. W., & Mitch, C. J. (2017). The Diffusion of Death: Romans 5:12 and Original Sin. Letter & Spirit, 12, 28.
Interesting
Christadelphians Origins Discussion 
It seems quite common now for brethren to make reference to the writing of Joseph A Fitzmeyer when explaining Romans 5 v 12. He is the one who suggests that the Greek “eph oi” in the verse should be translated as something like “with the result that”. So he would translate Romans 5 v 12 along these lines, “Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, with the result that (greek eph oi) all sinned”.
This misses what the passage above points out, which is that Paul has already spoken about “all having sinned” in Romans 3 v 23, and that in that passage it is referring to “actual sins committed by morally responsible persons”. Insisting that “eph oi” should be translated as “with the result that”, ignores the fact that in passages like 2 Corinthians 5 v 4 and Philippians 4 v 10 its meaning is clearly something like “because” or “for”. If we use this meaning in Romans 5 v 12, then when Paul says, “and thus death spread to all men, because all sinned”, it is simply a reference back to what he has already been talking about in Romans 3 v 23, which is our own inability to keep God’s commandments.
The passage above seeks to understand scripture by looking at its context, and this is surely the right approach, as opposed to the views of Joseph Fitzmeyer.
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I think I might have mentioned this here before – sorry if so. The New Testament, including Romans, is written in Greek, and the Greek-speaking experts of the Greek Orthodox tradition know a bit about it.
According to the Greeks and other Orthodox streams of Christianity, Western Christians *still* haven’t fully corrected Jerome’s and Augustine’s error with “for that all have sinned”, or “because all have sinned”, because we don’t look far back enough for the antecedent of ἐφ’ ᾧ. That narrow-focus error is common for people who are trying to operate in a language other than their own. According to the native Greek speaking scholars it should be translated “in which all have sinned”, i.e. in death. In other words, it’s the fact of death in our mortal lives leads us to sin. It’s all Greek to me, as Shakespeare said, but this makes good sense in the context.
There’s an entertaining learning-versus-confidence conversation on the topic at
https://hermeneutics.stackexchange.com/questions/14268/translation-of-romans-512
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