Modified Version—many thanks to Toran :)

‘Common suffixes that are used for making plurals are ’-들, -희, and -네‘. ’-네‘ is represented in ’우리네, 어르신네, and 영희네‘. When making plurals, the suffix '-네' indicates people are in the same situation or position. It’s appropriate to think of it as meaning group(우리네, 어르신네) or house(영희네). 

In the examples below, pronouns sound natural whether the word has ‘-들’ or not. 

For reference, 저, 저희들 are used for 존댓말(honorific language in formal and informal register in 상대높임법.) in comparison to 나, 우리들(non-honorific language)

1.나=I: 우리=we 

2.저=I: 저희(들)=we 

e.g 독감때문에 (저는) 병가중입니다. I'm a on sick leave because of the flu. 

e.g 저희는 고객 만족을 최우선으로 합니다. We put customers as first priority. 

3.너you: 너희(들) you 

너 뭐하니? What are you doing? 

너희(들) 뭐하니? What are you doing? 

 The hallmark of pronouns that have the suffix '-희' is that the suffix '-들' can attach to them. 

If we consider Collins Cobuild Advanced Learner's English Dictionary—"A speaker or writer uses 'you' to refer to the person or people that they are talking or writing to." It is possible to use you before a noun to make it clear which group of people you are talking to." 너 refers to the 'person', whereas '너희(들)' to the 'people'. 

4.이(this, it): 이들(these people, these men) 

e.g '이는 작년 동안의 판매 수치를 보여준다.' 'This shows sales figure for the last year.' 

5.그(he, that, it...):그들(they) 

"우리는 사실 관계에 관한 피고들의 세 가지 주장을 받아들인다. 그와 같은 사실들은 이 사건을 그 동안 제2511조 위반이 문제된 대부분의 사건들과 구별시킨다." 

"We only accept arguments relevant to the fact. The facts like such isolate this case from most of cases, which has been controversial against the breach of clause 2511." 

'이' as in '이 사건' is 관형사(che-eon modifier). 사건 is noun, which belongs to che-eon. 

che-eon is are comprised of nouns, pronouns, number words(수사) 

che-eon allows josa to attach to it. '그' as in '그와' is a pronoun having josa '와'. 

6.저(that):저들(they) 

7:자기(himself, herself): 자기들(they) 

e.g '그녀 자신은 그 회의에서 무슨 일이 일어났는 지 알 것이다.' 

'She herself may know what happened in the meeting. ' 

'그' in '그 회의' modifies noun(명사) 회의. Unlike pronoun '그' in 5, 그 was used as 관형사. 

In this case, 그 is a che-eon modifier. As I mentioned previously, che-eon(noun, pronoun, 수사) allows josa to attach to it, but 관형사(che-eon modifier) doesn't. 

Since 이, 그, 저 are arranged in order of farther distance, the nuances and usages of 이, 그, and 저; 이들, 그들, and 저들 are somewhat different.

For reference on the combination of '수사' and josa compare these two: 

'사과 하나가 있는 이 바구니에 사과 둘을 더하면 사과 세 개가 된다.' 'We have three apples if we add two apples to this basket containing one basket.'

'하나 더하기 둘은 셋이다.' 'One plus two is three.'

'하나', '둘', and '셋' are 수사. 세 is numerical determiner. '개' is bounding noun used with other numerical words. '에', '가', and '은',  '을', '이', and '이다' are josas. Here, '이다' is josa for predicative case, which describes the subject, '하나 더하기 둘', of the sentence.

Corrections are in Purple

Suggestions are in Green

Making Plural in Korean

‘Common suffixes that is raised for are used for making plurals is are ’-들, -희, and -네‘. ’-네‘ is represented in ’우리네, 어르신네, and 영희네‘. When making plurals, the suffix '-네' indicates people are in the same situation or position. It’s appropriate to regard it as suffix think of it as meaning group(우리네, 어르신네) or house(영희네).
In the below example examples below, pronouns sound natural whether the word has ‘-들’ or not.
1.나=I: 우리=we
2.저=I: 저희(들)=we
e.g 독감때문에 (저는) 병가중입니다. I'm a on sick leave because of the flu.
e.g 저희는 고객 만족을 최우선으로 합니다. We put customers as first priority.
3.너you: 너희(들) you
너 뭐하니? What are you doing?
너희(들) 뭐하니? What are you doing?
The pronouns having suffix '-희' have a hall mark A hallmark of pronouns that have the suffix '-희' is that the suffix '-들' can attach to it.
If we consider Collins Cobuild Advanced Learner's English Dictionary—"A speaker or writer uses 'you' to refer to the person or people that they are talking or writing to." It is possible to use you before a noun to make it clear which group of people you are talking to." 너 refers to the 'person', whereas '너' to the 'people'.
4.이(this, it): 이들(these people, these men)
e.g '이는 작년 동안의 판매 수치를 보여준다.' 'This shows sales figure for the last year.'
For reference, left words is are used for 존댓말(honorific language in formal and informal register in 상대높임법.)
5.그(he, that, it...):그들(they)
"우리는 사실 관계에 관한 피고들의 세 가지 주장을 받아들인다. 그와 같은 사실들은 이 사건을 그 동안 제2511조 위반이 문제된 대부분의 사건들과 구별시킨다."
"We only accept arguments relevant to the fact. The facts like such isolate this case from
most of cases, which has been controversial against the breach of clause 2511"
'이' as in '이 사건' is 관형사(che-eon modifier). 사건 is noun, which belongs to che-eon.
che-eon is are comprised of nouns, pronouns, number words(수사)
che-eon allows josa to attach to it. '그' as in '그와' is a pronoun having josa '와'.
6.저(that):저들(they)
7:자기(himself, herself): 자기들(they)
e.g '그녀 자신은 그 회의에서 무슨 일이 일어났는 지 알 것이다.'
'She herself may know what happened in the meeting. '
'그' in '그 회의' modifies noun(명사) 회의. Unlike pronoun '그' in 5, 그 was used as 관형사.
In this case, 그 is a che-eon modifier. As I mentioned on previous note previously, che-eon(noun, pronoun, 수사) allows josa to attach to it, but 관형사(che-eon modifier) doesn't.
For reference for on the combination of '수사' and josa:
'하나에 둘을 더하면 셋이 된다.' 'It becomes three when add two to one One plus two is three.'
'하나', '둘', and '셋' are 수사. '에', '을', and '이' are josa(조사).
Since 이, 그, 저 are arranged in order of farther distance, the nuances and usages of 이, 그, and 저; 이들, 그들, and 저들 are somewhat different each.

Another useful notebook entry, thanks Amy!  If you have questions about any of my suggestions feel free to ask.