Sponsoring my parents, a question of I-864

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Some background: I am a US citizen and living with my family(husband, kids and my parents), my sister is a green-card holder living with her family. Right now I am sponsoring my parents to apply for green cards.

I don't have income now and my husband won't take legal responsibilities to sponsor my parents. So my sister's family will be a joint sponsor.

I had worked from time to time in last three years(2013, 2014 and 2015). And my husband and I had joint tax returns. There means the total income on the tax return form 1040a is including my husband's.

This brings one question for the form I-864: In 19a, 19b and 19c,"My total income (adjusted gross income on Internal Revenue) shall I write down my own incomes from my w2s or the total income on joint tax turn form 1040a for the recent three years", shall I fill in with my own income from my w2s or the family income from our joint tax return form 1040a?

Thanks!