I saw the spoiler and found out the secret (real reason) but for the sake of not ruining the story, let's just follow the context that were released in recent manga translations for now.. MC will head to the academy in the capital and won't be able to return to their territory for few years until graduation just like his siblings.
Based on the translated chapters you could also assume his ice magic is so special so he could be targeted for that as well
Regarding your two ideas, the timing does not fit. The parents were sad of loosing him, nearly right after his birth and at that time his siblings were still at home, and he was not able to wild ice magic.
I checked the chapter 1, was it right after he was tested in the church? The parents were worried for him that he might be targeted since he is special since the crystal ball for testing magic cracked, which means his magic power is special or he's strong but not detected by the church people since they were all focusing on his water magic attribute that seems weak for them.
Does anyone know?
Why he whole family acts like their time together is very limited, and they will never see him again?