I am a medical student at MCW and they say that we must either be on our parents or our spouse's insurance. Otherwise we have to purchase from them. Is this legal? Can't I purchase insurance on my own and just meet whatever minimum requirements they have?
Full-time MCW students are required to have health insurance but it can be through their parents, their spouses or their full-time employer. Regardless of how you are insured, proof of your insurance will be required.
Those not otherwise covered by insurance ARE required, as you say, to enroll in the MCW plan (the annual premium is paid by the College for all full-time PhD students). You can acquire, at your own expense, insurance under the same MCW plan for your spouse and family.
It is legal for MCW to have as a requirement that their students be insured.