Legal Question in Wills and Trusts in Pennsylvania

I don't know what it means to be a co-signer on a bank account. Either there is a joint bank account holder or the sister had power of attorney and was authorized to sign. If she was a joint account holder, then all of the money in the account passed to her as of date of death and the money belongs to her, unless you have real rock solid evidence to the contrary.

If this was not what your father wanted and you have no evidence, its too bad, but then he should have not done poor man's estate planning like this. He needed something else besides joint accounts and that is what a power of attorney is for. So your sister does not have to share information about the accounts with you if the money now belongs to her solely as the surviving joint account holder.

I'm sorry- don't mean to sound flippant or rude and its not what you expected to hear. To be on the safe side, I suggest you find a probate attorney who practices in the county/state where the estate for your father is pending and pay for a 30 minute consult to verify what I have stated (which was based on the assumption that your father's estate is pending in PA - if elsewhere, laws may vary and it might be possible to bring the money into the estate if needed to pay bills).