I have a theory on this. I think Kalim has been kept in isolation because he's supposed to be the face of the Asim family. Think about how he acts and how ignorant he is. That is not normal for an heir.
We could just chalk it up to Kalim just isn't that smart, but I don't think that's it. I think the Asim family had some really messed up intentions with Kalim. I've been sitting on the fact Kalim is 9 months and 13 days younger than Jamil, which had some really UGLY implications about that there, but it feels more and more like Kalim's family treats him like a PROP or an OBSTACLE.
He had to be born fast because there wasn't an Asim for Jamil to serve. He has to be this clean and innocent face to cover up the very dark undertones of what the Asims do behind closed doors. Kalim is supposed to be head of the family yet knows VERY LITTLE of business or politics... That's... That's not how you do business. You have to be on top of and aware of anything that could screw up your business. Instead, he's a very sociable, cheerfully naive guy who can endear people to him because he does genuinely care, even if his understanding of issues is misguided or ignorant.
I think Kalim is meant to be the face when he inherits, but there are other siblings who are being trained to play in the political world or do other... less than savory things for the family and Kalim is kept ignorant because if he doesn't know, the Asim family can use him to claim innocence if someone gets caught.
Say a younger half-sibling gets caught doing something majorly illegal in the Scalding Sands. Well, if Kalim, the head of the Asims, doesn't know, it's easier to claim that the sibling did something on their own and the rest of the family wasn't involved. That would also explain why relatives are trying to kill him.
My theory is the assassinations come majorly from the mothers of his half-siblings. Originally, I thought it was so that the majority of the inheritance will go to their children first instead of Kalim and his full blooded siblings, but if Kalim is the face, that puts a new perspective on it.
What parent wants their kid to be considered disposable if something bad happens? No loving parent wants to watch their kid go to jail, or worse, be executed. Death of a child is a very painful experience that no parent should ever face, but knowing your child is being raised to do something potentially illegal to lift up your family only to be cast aside if they mess up somewhere because they aren't the future head?
And it's likely Kalim is kept unaware of this. I think he's been set up by his family to be what is basically a puppet ruler. Yes, we see Jafar puppeteers the Sultan in Aladdin, but Japan has a HISTORY of puppet emperors. Emperors who were emperor in only name and had to constantly do what other people around them wanted or else they would be replaced with a younger, more malleable replacement.
Like I don't feel like getting into all the dark theories today I have about how things are set up in like The Scalding Sands and the Kingdom of Heroes and how come Riddle's mom gets away with her abuse in the Queendom of Roses, but I do want to point out that a lot of these issues aren't the complete fault of these teenage boys.
A lot of their issues are stemming from the way society has been set up to fail all of them and the fact the adults have done very little to step in and fix or change it. Yes, the boys are responsible for their actions, inactions, reactions, and how they choose to respond to these issues, but a lot of these issues, particularly Jamil and Kalim in particular, are a microcosm of the issues in their societies.
There is no good, moral reason Jamil should have been born into any servitude, especially one that is inhumane enough to force kids to be poison testers.
There is no good, moral reason Kalim should be having to live in constant threat of being murdered by his family.
There is no good, moral reason Riddle's mom got to continue to abuse Riddle the way she did.
There is no good, moral reason Leona has been made to feel hated and despised in his own home.
There is no good, moral reason Azul had to endure horrendous bullying with no adults stepping in to stop it.
There is no good, moral reason Vil has been typecasted constantly as villain just for being ethereally pretty and good at his job.
There is no good, moral reason Idia's family was doomed to start to lose their magic if they aren't constantly depressed or negative.
There is no good, moral reason Malleus was blessed (read: cursed) with magic that made him so much more freaking isolated that he already was due to the loss of his parents to war.
And as far as we can tell, not much is done by the adults in charge to change the world to be better for their future generations. And that's heartbreaking.