The student (not sure if that’s you, or if you are the dad) should apply to colleges that do not ask for the step-mother’s income. You’ll have to email each financial aid office separately to get answers. But I am not sure if that exists, or even how that would work if the father and step-mother file taxes jointly and/or if their assets are held jointly.
In any event, this would only be a concern with schools that use the CSS Profile to determine eligibility for FA. Schools that use ONLY the Fafsa will not ask for financial income from the non-custodial parent at all.