The purpose of asking for tax records is to establish total income earned.

If your parents are unable to provide tax records, they should provide alternative documentation, such as a statutory declaration on how much they earned in the period requested for. Note that income does not merely refer to employment income. It also includes income from trade, investments (such as rental income and dividend income) and business, amongst others.

If the statutory declaration is made in Singapore, your parents should sign it in the presence of a Commissioner for Oaths or Notary Public as witness.

If the statutory declaration is made in a Commonwealth country, your parents should sign it in the presence of a Notary Public, Justice of the Peace or other authorised person under the law of that country as witness.

If the statutory declaration is made in a country that is not part of the Commonwealth, it will have to be made before a consul, vice consul or other authorised person under the law of that country as witness.