Did your dad have any documentation organized somewhere - like a file folder or safe deposit box list? When my mother passed, I found she'd actually left a spreadsheet with account numbers and institution names (though not passwords, thankfully), which saved me weeks of detective work. The estates departments at banks and brokers are genuinely your best resource - they've handled this hundreds of times and know exactly what paperwork they need from you. What made the process smoother for me was gathering everything upfront before making calls: original death certificate, your executor appointment letter from probate court, and a list of institutions if you can find one. Some places will let you initiate transfers online with certified documents, others will insist on certified copies mailed in, but they're legally required to help you once you've proven your authority.