I am in Colorado, so I am not able to answer your questions specific to IN law, but I hope this will help guide you in the right direction.
As to locating a will, I would start with the attorney, if the will was drafted by an attorney. If you are not sure which attorney drafted the will, sometimes the local/county Bar Association can assist. Otherwise, maybe check the safe of the decedent or safe deposit box at a bank. If you cannot locate the will, then the estate will be distributed intestate. Intestate laws can vary by state. I recommend contacting a local attorney for a more specific answer to your state. Intestate means that the estate gets distributed to the closest living relative. Usually, it will be distributed to the decedent's bloodline first, and if there is no one left, then the bloodline of the decedent's parents.
Usually, if someone is listed as "and" it means that they both have to sign. If listed as "or" of the two signatures will suffice. However, this can be handled differently by financial institutions and the "and" could really be an "or". It is best to check with the financial institution how the account was set up.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.