A: You should be able to call the Social Security Administration and they can search using an Alphadent query. They'll need his full name, DOB, place of birth, parents names, and mothers maiden name. Protection under the Privacy Act ends upon death, so they should be ok to release it. At least they were when I worked at SSA 10 years ago.
A: That is not true. What might be confusing her is the general rule that an individual seeking Social Security Disability benefits needs to have worked 5 of the 10 years before their disability onset date. There is no such rule for SS Retirement benefits. You just have to have worked the equivalent of 10 years over the course of your lifetime.
A: Her SSDI payments are for her disability and she is under no legal obligation to tell you. Besides the moral and ethical issues, it would also pose a tax issue if she knowingly withheld that information from you while you filed an erroneous joint tax return.