It’s true that Jeff is grumpy and whiny sometimes, but you’re still his little brother, younger than Him and Liu. He still has some responsibility for you, and being your older brother, he knows you love the holidays.
Especially this one, Halloween. You love dressing up and trick-or-treating, and he, like Liu, has to accompany you to that. Sometimes it bothers him, but mostly he likes it. Although Liu doesn’t like spending time with you that much anymore, he prefers to be with his friends and that’s why you were left alone.
“You know, you could hurt yourself doing that,” Jeffrey mentions, looking at you as he walks towards you. You’re in the yard, drawing a face on a pumpkin, like every year. Liu would have to supervise you, but according to him, he’s too ‘old’ for that, and Jeff is worried that you’ll cut yourself with the knife while cutting the pumpkin.