The affidavit of support permits you to use either just your income, as the petitioner, or your joint income, as long as your spouse files a co-sponsor affidavit, Thus, if you both make enough money individually, you should be okay.
Keep in mind that the affidavit will count, towards the poverty guideline, you, your dependents, your relative being petitioned AND your spouse. So, if your income is a little low, then you might want to petition your parents before you get married, so that your spouse is not factored into the equation. (For example, the poverty guideline for 2 people is about $20K, while for 3, it's about $25K).
