From what I remember, you're not guaranteed to get both traits in vanilla anyways. The childhood focus you pick simply increases the chances of a child getting one of those traits, unless the GoT mod team changed that for this.
I feel like they did change it. For me, I have rarely, if ever, received both childhood traits from a focus selection. For example, if I pick Pride, I'll receive either Haughty or Brooding, but never both. In original CKII, it's true sometimes I would sometimes receive neither trait, but many other times, I'd receive both.
AGoT also seems to always provide three childhood traits, with one of those three being from the focus you selected, but again, never the two from the same focus. Therefore, this would be my advice to everyone playing AGoT:
Always pick Duty for everyone. You're guaranteed to receive Conscientious because it's the only possible selection, and it will always result in either the Diligent, Temperate, or Just traits. Diligent and Just are especially good in AGoT, because they give +1 learning, and learning is crucial to promoting a stronger educational trait. The guardian trait associated with Conscientious is Just, so make sure your educator has Just. In vanilla CKII, the downside to Conscientious is you don't receive as many childhood educational traits, but in AGoT, you always seem to receive three, so this weakness doesn't apply to Conscientious. Furthermore, vanilla CKII
improves the chances of acquiring a better educational trait with the traits Diligent, Quick and Genius, although I can't confirm whether this applies to AGoT yet.
Anyways, the whole Conclave educational system needs a rework in AGoT. It's not working the same way at all from vanilla CKII, but whether this was intentional from the developers or not, I cannot say. I'm just not sure I agree with the vision of AGoT's way of handling it.