Becoming an "A" student of the I-864 and instructions will help.
I would not try to combine income with your son. Doing so would require him to sign an I-864a. I would:
1. You, as the primary sponsor (you will always be the primary sponsor), submits an I-864 with household size of 4 or 5 (you, 3 kids, new immigrant). If your income is not sufficient, then :
2. Father (JOINT sponsor) also submits I-864 with household size of 3 (Joint sponsor, his spouse, new immigrant)
- Joint Sponsor spouse completes I-864a to combine income with Father.
You do NOT combine income or household sizes between households.
Note: Unless a person is self-employed, past tax returns have nothing to do with current income or ability to support a new immigrant. CURRENT annual income is king. Current annual income is calculated as follows:
current pay period gross pay sub income multiplied by number of pay periods in 12 months. Example $1,000 income on weekly pay stub equals $52,000 current annual income.