There is a one time death benefit of $255 from the SSA. It is usually for surviving spouse and child. I am not sure for adult child, the parents can qualify.
I am not sure what you meant by refund of his social security and medicare benefit. These taxes are deducted from payroll taxes on wages. They are contributed to a pool of insurance for all taxpayers who participated. If he passed away, his contribution, the payroll taxes deducted remain in the pool to help other participants.
As to your situation for funds and source of money, there could potentially be a relatively large wrongful death issue and compensation issue, apparently, considering where he passed away at his young age, which you may want to consider to consult an attorney who practice in the area.
Please feel free to follow up.
Fiona Chen, MPA, Ph.D., CPA, ABV, CFF, CITP