My brother-in-law was career Army Reserves. He has recently been diagnosed with terminal cancer. Where does his family contact for care?

Other than his regular provider? Your BIL eligible for VA Medical?

You may need to provide more context to your question.

If you are wanting VA services it would be determined by whether or not your Brother in Law is eligible. If he is then they need to contact the appropriate tab on the VA website.

There are options for everything from healthcare, life insurance, graves/burials, service member benefits, family member benefits and more.

If he is eligible for service he would need to register and start the ball rolling. If he is already eligible and registered then call the appropriate point of contact to answer your specific question.