unfortunately, I don't see this as complicated.... .....best to run your scenario through the IRS tool to determine if your son and your grandchildren qualify as your dependent.
https://www.irs.gov/help/ita/whom-may-i-claim-as-a-dependent
if yes, then there is a dependent credit of up to $500 available and the medical expenses are deductible as long as YOU itemize and only the part of the medical expenses that exceed 7.5% of your income qualify.
Living expenses (rent, food, clothing, insurance) are never deductible
