두번째 일기 : 가족

안녕하세요!  
오늘 일기는 제 숙제예요.

("오늘 저의 숙제는 일기를 쓰는 것이에요." You are not wrong, I just trying to make sentence more natural) 

우리 가족은 모두 아홉명이에요.
어머니와 아버지가 계시고, 남동생이 한 명 있고 여동생이 한 명 있어요.

(If you want to make this sentecne short, you can say, "남동생, 여동생 한명씩 있어요" and I am going to explain something about names of siblings:

동생 is younger siblings and you can differentiate between female and male as 여 and 남 in front of the 동생. what you wrote is correct.) 

When it comes to older siblings,

when you refer to older sister as a younger sister: 언니

when you refer to older sister as a younger brother: 누나

when you refer to older brother as a younger sister: 오빠

when you refer to older brother as a younger brother: 형 

모두 같이 살아요. 그리고 오할아버지와 오할머니 하고 친할아버지와 친오할머니가 계십니다.

(외할아버지,외할머니, 친할아버지, 친할머니) 

남동생은 공장원고 (It doesn't make sense; you can say like this; 공장에서 일하면서 공부하는 학생이에요.)  여동생도 학생이에요.  저는 회사원이지만 공부를도 하고 싶어요. 

I'll write in English too, so there's no mistake about what I wanted to say:

My second diary: family
Hello!
Today's diary is my homework.
My family consists of 9 people altogether. There's my mum, dad and then my younger brother and sister. We all live together.
There's also my grandpa and grandma (my mum's parents) and my dad's parents.
My younger brother is working in a factory and studying, and my younger sister is also a student.
I'm an office worker, but I want to study too.


***
Is there a shorter way of saying "I have one younger brother and one younger sister" ? What I wrote seems so long!

AND I'm still very confused about how should I address/talk about my younger siblings, in a situation when they're both younger but one is male and other is female, so people know which one I'm talking about? Is there any other way than how I did it above?

Also, how should I end a diary/letter/post in Korean? Something like "See you" , "Thanks for reading", something to end it?

Thank you!

두번째 일기 : 가족

안녕하세요!
오늘 일기는 제 숙제예요.
우리 가족은 모두 아홉 명이에요.
어머니와 아버지가 계시고, 남동생이 한 명 있고 여동생이 한 명 있어요.
모두 같이 살아요. 그리고 오할아버지와 오할머니 외할아버지와 외할머니하고 친할아버지와 친오할머니가 계십니다.
남동생은 공장원고 공장원이고 학생이에요.

제 남동생은 공장에서 일하는데 동시에 공부도 하고 있어요. is more natural.

여동생도 학생이에요.
저는 회사원이지만 공부를도 하고 싶어요.


I'll write in English too, so there's no mistake about what I wanted to say:

My second diary: family
Hello!
Today's diary is my homework.
My family consists of 9 people altogether. There's my mum, dad and then my younger brother and sister. We all live together.
There's also my grandpa and grandma (my mum's parents) and my dad's parents.
My younger brother is working in a factory and studying, and my younger sister is also a student.
I'm an office worker, but I want to study too.


***
Is there a shorter way of saying "I have one younger brother and one younger sister" ? What I wrote seems so long!

AND I'm still very confused about how should I address/talk about my younger siblings, in a situation when they're both younger but one is male and other is female, so people know which one I'm talking about? Is there any other way than how I did it above?

We don't know, you should mention that.

and when we say that, it is short. 남동생, 여동생 하나씩 있어. like that.

Also, how should I end a diary/letter/post in Korean? Something like "See you" , "Thanks for reading", something to end it?

hmm........... there are so many..

in that case.. "또 쓸께, 안녕" is good.

Thanks!!

두번째 일기 : 가족

안녕하세요!
오늘 일기는 제 숙제예요.
우리 가족은 모두 아홉 명이에요.
어머니와 아버지가 계시고, 남동생, 여동생 한명씩 있어요.
모두 같이 살아요. 그리고 외할아버지와 외할머니 하고 친할아버지와 친할머니가 계십니다.
제 남동생은 공장에서 일하면서 공부하는 학생이에요
여동생도 학생이에요.
저는 회사원이지만 공부도 하고 싶어요.

또 쓸께, 안녕! ^^

**I hope I got everything ok, thank you! ^^