möb is so cute haha
it's a little ambiguous but it counts as a kill when you try select *take away their drink* and they fold in on themselves
Viewing post in [SPOILERS] Guide for the end of genocide route
Both are killable in a normal run. For Mobius you just have to choose enough mean dialogue options before they show you the bottle of Gintegral, and then after showing you the Gintegral your options will be [what even is that?] and [that looks disgusting] (you'll get different dialogue options if you were too nice lol). Then regardless of what you choose afterwards, you'll eventually progress to [future you sounds miserable] or [*take away their drink*], the latter of which kills Mobius.
For Alexandria, when she asks if she can talk to you about her problems, choose [no] and your next choice should show up as [okay?] or [sounds obsessive]. Either will work, and same thing for the dialogue choice after that, and then you choose [you are being dramatic] > [I still think you're insane.] > [*grab one of the horns.*] which kills her :(
yeah they aren't really explicitly "killed" but you can always confirm you're on the right track with equality's reaction. he usually tells you to stop or expresses some form of pain when a concept is killed.
like synthbutterfly said for alexander horned sphere the option is literally *grabs one of the horns*