About applying citizenship of Japan

I am here since 12 years.
My visa history is: 7 years enginner,5 years spouse visa history.
I hold 3 years spouse visa currently.
I can read & write Japanese too & having N2 language certificate too. I am going to apply for citizenship.
As per some list, homukyoku asked for
Taxation certificate(課税証明書) & Tax certificate slip(源泉徴収票) of all members included in the Juminhyou.
Now we are 5 members in Juminhyo including myself,my wife,my son, father-in-law, wife's brother.
They need it because if the applicant is unable to earn in future
due to some reason, so homukyoku want to see whether applicant is able to survive with the income of
other family member.
I can get those document except wife's brother because my wife dont have much good relation with
her bother. My wife is working, I have good income already. Why they need brother-in-laws doc? I asked homukyoku, if I cannot give the document of wife's brother then am I not eligible for citizenship?
Does my eligibility depend upon wife's brother's income certificate? Homukyoku told thay I can apply, but after submission of documents,it depends on daijin who take this decision.
He may or may not ask wife's brother"s doc too.
Anybody has opinion or knowlege on this?

They said if they need your brother-in-law's information, they will ask for it. Not sure what more there is to say.

there are two solutions.
1. you (or your wife) can get 課税証明書 of brother-in-law at city office without his permission, because he and you are members of the same family, on the basis of 住民票.

2. you can separate one 5-member family to two families.
go to your city office.
私と妻と子供を別世帯にして下さい。
they will separate 5 members to 2 (father-in-law and brother-in-law) and 3 (you, your wife, and your son).
get a new 住民票.

Firas, Thanks.
Ken-san, I think you gave nice idea. That can be done. We want to avoid brother-in-laws document. As you say, any member from juminhyou can can get kazei shoumeisho without permission. But I think that may be bad, I will ask my wife. But we have to depend on him for his 源泉徴収票.

Ken-san, your option no.2 is possible. Right? Thanks for that. I also dont want to trouble anybody for getting the document.