Ed meeting up with his father, Hohenheim, is interesting because you start to see why Ed dislikes his father so much. There appears to be no sense of guilt for leaving the family in the condition of things as they are. The way he talks is nothing you would expect of a father. One thing he is right about is the Elric brothers’s reason for burning down their house. While there is no turning back, it is in part their failure that they don’t want to be reminded of. Pinako was on the money on one thing: those boys needed their father, and he failed at that.
A bit more focus on Lin, and we see that he is technically a prince; it is a bit more complicated than that. Funny enough, like the Elric brothers, he has an awkward relationship with his father. As there is zero love in their relationship and they are among 50 clans, he needs to win favor. Which is the only reason he is seeking immortality. A showcase of how both fathers have forced each of them to seek things beyond the natural course of life.
One of the foundations of alchemy that we were shown since the start is the idea of equivalent exchange. Hohenheim mentioned, What if what Ed & Al created with alchemy wasn’t their mother? Which turns out to be the case. At first glance, it is a big failure that they sacrificed for something that was their mother. A huge revelation is that alchemy utilizes the living and the living only; the dead can’t be brought back. Which shows the mistake they made by even attempting to bring back their mom.
Still, this means that Al’s body, for instance, is in a pool of the living. When you also consider Al still has his memories from before and after the attempt to bring back their mother. So while there is no way to bring back their mother, it does mean it is very much possible to get Al’s body back. It is also good for Ed to tell their teacher the results of their research. She tried to bring back her baby or for that baby to die. At least her baby never died a 2nd time.
Ed’s plan to use Scar to lure out the homunculus is interesting. It makes sense that both he and Al get called “their dear sacrifice”, so if they were to face actual danger, they would interfere. Quite the bold plan, but it would work if they can hold up against Scar, which is the big danger. Though thinking they would even lure out Wrath might have made this lure even more successful.