Honestly, she’s like that shitty friend who always goes back to her shitty boyfriend and...

He's always in unnecessary danger because his mom is always in unnecessary danger

I laughed because that is so true he’s been in danger like five times?

Talking about wanting his dad back. Yeah, because he saved you about 5 million times now you'd be a dead child

They are both written to make Killian look better than he is and accommodate his toxic behaviors and mentalities. They are not independent characters because almost all of their thoughts, actions, reactions, and behaviors fluctuate around allowing the plot to tolerate Killian’s toxicity without making him look like an outright villain.
Demian has no personality beyond random kid doing kid things. He exists to physically and psychologically tether Rowena to Killian. To further this end, he immediately becomes attached the second he meets Killian, making puppy eyes at the mom who worked her fingers to the bone struggling to raise him because he just doesn’t feel fulfilled without a barely present paternal figure who basically just played ball a few times. If Rowena had been alone, it would have been far easier to escape and live untraceable. Even his illness is just to make it difficult for Rowena to escape. The medicine is conveniently difficult to acquire, allowing Killian to grant or withhold it at his convenience, further pressuring Rowena to engage with him. 99% of scenes and plot lines directly related to Demian are A. Father son bonding, B. Illness that is a roadblock to Rowena’s independence/requires Killian’s assistance, and C. “I wish I had a dad/I like Mr. Ghost/I like the Duke more than your other, objectively less toxic and traumatic potential love interest”