My father died in 1995. Last Sept. I received a letter from a company that locates heirs. It seems that he had invested some funds that nobody knew about and through the years it has added up to a reasonably substantial amount. My Brother-in-Law and his two sons are also listed as heirs. (My Sister died in 2006.) I have signed the agreement from the company, but the others won't participate for reasons unknown to me. I have been estranged from my family for many years. As far as I know, there is no will that has been found. I have checked out this company, and they are legit. Do I have any options here?

There are companies that do this and they will receive a percent of the funds, Have you not merely tried to find out where the funds are, if this company found them, then it has to be some public record of the money.

Ask them to get our share of the money then,

Fr_Chuck is correct. A thousand years ago, during college, I worked for a man who searched public records for unclaimed funds and paid me to type form letters to potential beneficiaries/heirs. His cut was a third if the person was successful in obtaining the funds. Especially with the Internet at your disposal, you should be able to find this money on your own and claim it. Usually it takes only a copy of your birth certificate and maybe a copy of your SS card to make a claim.

Google with the keywords "unclaimed funds" (without quote marks) plus your state name. That might be enough. Or check with the reference desk at your local library for other hints and helps to find "lost" funds.