You have to serve at least 180 of active duty other than training (boot camp don't count for credit) to be considered a veteran.
Someone who is a reservist and who deploys in support of the war can become eligible for certain benefits. Some returning veterans can receive health care at the VA for up to 5 years. (I work at the VA)
There are many different benefits that people qualify for that deal with health care, home loans, small business loans, education, vocational rehabilitation, VGLI (veterans life insurance), and compensation. It depends on many factors.
1. length and character of service
2. War time/Combat service
3. Disability caused by service
4. Retirement/ or non retirement
5. What period of service (WW2, Vietnam, Korea, Iraq)
there are too many factors to name.
Your father in-law should contact a veterans service organization. He can also contact his VA regional office. He may need to have a lawyer to assist with filing an appeal.
I put a link to the VA website you can see what types of benefits are there and see what the eligibility is for them.