Son saying upsetting things

My son has started to say some things that I would classify as upsetting and disturbing… For example, my father (his grandfather) is battling cancer and spent over a month in the hospital due to a septic infection. My son will FaceTime and ask his grandfather how he’s doing, which makes my dad’s day, but when my dad responds that he’s feeling good/better, my son expresses displeasure in the response and says “Noooo! I don’t want him to get better.” “Aw man, I want him sick. I want him gone.” I did have ‘the death talk’ with my son after our cat was hit by a car a few months back. I explained that sometimes when living things get really old, really sick, or really hurt they die meaning they go away and we can’t see them anymore. That’s why we have to be careful and do our best to take care of ourselves and each other, and try to help those we can, etc…. So, I’m not sure if this is just a phase, he just doesn’t fully understand, he thinks he’s being funny by saying the opposite thing, or if he in fact wants his grandpa to die. I’m almost wondering if it’s like a twisted abandon issue - where he’s trying to distance himself or try to control the situation on his terms. Like, if my dad does end up passing, it’s ‘because my son wished it’ and not like he spontaneously left him. I’m not sure…. Obviously it’s a very sensitive subject to me and his responses/actions really upset me. I tried talking him through it, trying to re-explain, ask him why he says that and why he feels that way, trying to install a bit more empathy in this kid, but I feel like I’m not really getting through… One another note, the other day he saw a cockroach outside and yelled for me to “come kill it with a knife.” In our household knives are used as utensils for eating, so I’m not sure where the weaponized comment came from. He was explaining to me that I needed to stab it and cut off its head, etc… He’s normally a happy, bubbly, sweetheart who just wants to have fun and make everyone laugh, so I’m not sure where this ‘dark attitude’ is suddenly coming from. He does get some limited screen time which is screened/monitored to make sure content is appropriate. He does go to daycare/preschool. Not sure if he’s picking this stuff up from his classmates or what.. I’m def going to have a talk with a teacher. Advice/suggestions would be appreciated.