as long as you can justify that you support over half of their e

If you don't support their medical expenses, and they end up have some, that should be included in the calculation for 50%. For example, their total expense without medical care for the year is $10,000. Medical expenses were $2,000. Then if you provided more than $6,000, you can claim them as dependent.

Most likely, IRS is not going to audit you for that. They have much bigger fish to catch. Unless someone else (like your siblings) claim your parents as dependent also.