Every state has a set of laws called intestacy that governs what happens if a person dies without a will. The laws will determine which of the next of kin receive what property in what percentages. Retain a probate attorney in the state where the individuals died to review the probate documents and real estate documents to determine what needs to happen and how many estates to raise.
Mr. Bernick gives a good answer. I would note that, asssuming son owns everything outright at the time of his death, what happened to mom and dad is very well irrelevant. It only matters what he owns and who his heirs at law under the laws of intestacy are. If the son died without a spouse, children/grandchildren or parents (yes)/grandparents then the estate would likely go "outward" to siblings, aunts/uncles, cousins.
This is not legal advice nor intended to create an attorney-client relationship. The information provided here is informational in nature only. This attorney may not be licensed in the jurisdiction which you have a question about so the answer could be only general in nature. Visit Steve Zelinger's website: http://www.stevenzelinger.com/
By state statutes as explained.
You will need a probate attorney to assist you.
Your question isa good reminder that everyone needs to do estate planning.
Also-Living Trusts should be considered to avoid probate.
The answer given does not imply that an attorney-client relationship has been established and your best course of action is to have legal representation in this matter.
Every state has laws of intestacy which govern situations like this. The property will pass according to the relevant state statutes. Likely, the individuals surviving spouse (if one) or children (if any) will take the majority of the property. If there is no spouse and no children, the individual's siblings, grandchildren or more distant relatives may be entitled to a share in the estate. You should contact a RI attorney to discuss the specifics.