@sbpilates
I think you are too busy worrying. I have already outlined several steps.
Start with the broker he used in 2021. If you don't know the name of the broker, then get access to his bank account and look for the large deposit you think is there. Then go to the broker and ask for copies of his statements and his 1099s. If the broker didn't issue any 1099s ask why. The statements should show you the gains and you can calculate the tax using the statements if you don't have 1099s.
Wait until Feb 10 for any current year 1099s or W-2s. If they don't come, go back to the bank statement and look for more deposits coming from an employer or broker. Then contact the employer for a copy of the W-2.
If you haven't already checked his home for account statements and records (bank, broker, employer pay stubs, checkbook, etc.) you should be doing that soon. He would at least maybe have a debit card in his wallet if he passed away suddenly, that could be the key to the bank, and the bank will be the key to everything else.
For each business you need to contact, you will probably need to send them an official (certified) copy of the death certificate plus a copy of your appointment as personal representative. You may need to order extra certified copies of the death certificate from the registrar.
