Can One Find Adult Dependents using ACS or PUMS data

I have been asked to come up with a number for adult dependents (i. e., not the householder or spouse, 18-65 years old, financially dependent on the head of household/spouse).  I do not believe that ACS data lets me ask that question directly.  Using PUMS (OPUMS in my case) it might be possible to infer a number by looking to groups such as persons who meet the criteria and attend college or graduate school or who are disabled and unemployed.  I have also looked at IRS data but so far have not found any tables that would speak to the question.

Does anyone have suggestions for how to manipulate ACS or PUMS to get at this question or other data sources that might be on point?