What's Wrong with Sharing!?

hello there, good to see ya :)
I'm feeling quite good today. why ? I don't know. I just feel that way. yah, you know sometimes our heart feels good without any cause. just think this as a good luck :P

well out of that chatty-matty talk.
I'm picking up a case in my house (well it's not that I have a bad condition in home) that my family, or objected to my sister and mother, don't want to share.
rude? Impolite? noo, I don't mean to mock at my beloved sister and mother.
I just hate the way she (or sometimes they) see the eligibility or the level of appropriateness of sharing.
it means she or they sometimes don't show a good way of sharing things with some people that in this case is people out of our family or our non-relatives.

In my house, there's a man staying as our worker (my dad has a shoe shop so he has some workers). let's say his name is Willy. because he isn't our family, he tends to stay silent or not get in our way (our family I mean). even just to drink, he ask permission. Oh God, I don't like that way, it's a bit too decorous and I don't like that. so that's him.

now's time to talk about my sister. She is 22 years old currently, and has finished her undergraduate study in UGM or University of Gadjah Mada. now she's working independently, selling things but still stay in our house (yeah she's single), and she did a REALLY good job in maintaining her own shop.

our family is a really busy family. Dad and Mum go to work at 8 and come back at 6, 7, 10, midnight, or even the next day sometimes. and all that happens between the time is only work and work. we are selling shoes in dozen, scores, or in a big amount simply so we need to maintain a REAL bunch of shoes. thousands of shoes. and that's what we call busy. my sister usually helps my parents (she also open her shop there so it's like hitting two flies at once). my brother and I also help my parents but not as usual as my sister because we still have a lot more to take care of (we are entering university next month. pray us luck ! ;) ). what we can take from here is that we are lack of time to do housework especially cooking. so we often call for delivery service from some fast food restaurants.

now this is the problem.

when me my brother and I in home without my parents, we often called for delivery (it's usually pizza), there was once that we ordered 3 lasagna and 1 pizza large size. that time, I ask my sister :
I: why 3? how 'bout dad and mum and willy?
she: dad and mum is going home late.
I: how bout willy?
she: well he can take the pizza.
I got a bit bad thought of that, but I didn't take that as a matter. well some minutes after that, he came back home (the workers go back home, but my parents are still going to go to our 2 restaurants, well to take a look as usual. and yes we have 2 restaurants). after coming back home, he as usual went to garage tidy up the shoes (our garage is the shoes storeroom). because I was going to eat the lasagna, I cut the lasagna into half. then I asked my sister :
I: this half is for him. whadaya think ?
she : dont give it.
I: ??? why not? he deserve to have what we eat.
she : just eat it, dont you give it to him. he can take the pizza instead and it's enough for him

WTF, i thought. what's wrong in sharing !???
and it didn't happen just once. it often happened. I think she don't have the right to say that because:
1. it's my food so it's okay for me to give it.
2. he has the right to eat what we eat in the name of human right.
3. didn't she feel some hesitation in her heart that she decided not to share ?
4. if she were him, what would she feel when she heard that?
since that time, I less respect my sister because of what she did. why? because I told her many times but she didn't hear. ck, I need to be patient. I'm so fed up.

P.S. : this is a secret between us, don't tell anybody okay? ;)