Do you ever kill a sim because they’re just okay?

Yes I have but not direct family members though

One time in my Levi legacy, Vlad snuck in to the household at night and drunk from my heir sim at that time. Off course it ruined her chance of getting a promotion before elder-hood, so I had her go on a revenge quest to get Vlad to come to her house and trap him under the sunlight by indefinitely cloud-gazing with him :D >:)