Hey,
you are actually getting wrong meaning. In india, If someone is earning more than 2,50,000 rupess than they have to pay tax.
My brother is already filing tax return. my father is retired in 2015. he is completely dependent on me and so is my mother.
I'm pretty sure I did not misinterpret your now deleted post.
1. You had asked if your brother should file his tax returns for the last two years. BTW the time limit for filing taxes is one year. This means your brother cannot file his taxes retrospectively for the last two years.
2. Even if someone's income is below the taxable limits, s/he must file their tax returns as 'Nil returns'.
3. You mentioned your brother does not deposit his money (income) in a bank account. This makes it seem like he is paid in cash, no taxes, not deposited in a bank account and cannot be traced.
4. You asked if IRCC will ask for proofs if your brother states he is getting married. This seems like a false reason to return to India.
If your brother is earning less than the taxable limit of INR 250,000 then it means his monthly income earned from his business is less than INR 20,000 which is extremely low.... both in terms of finances for his visit + as an employment tie to return to.
I still recommend your family must sort out their financial and tax situation before applying. It's their choice of course