The FAFSA experts can correct me if I’m wrong, but I think FAFSA counts a married couple living with the student as “parents” financially, and discounts the non-custodial bioparent’s household situation. I think the assumption is that if two adults are in a marriage, both act as co-parental figures to the child regardless of biological/adoptive parent status.
Therefore, your most recent now-divorced husband would have had his income included with yours as her financial custodians if you two were still married. It wouldn’t matter to FAFSA whether or not he legally adopted your adopted child. The same as if you had a biological child and married a man who was not her bio-father - for FAFSA, his income and assets would be counted.
Now that you are divorced and he is not living with the child, his finances do not matter for FAFSA.
OTOH, I imagine this scenario might possibly be a little stickier when filling out the CSS Profile. But I’m not sure.