If they did not setup Legacy contacts (people who can access their account after their death), you will need to either gain access by resetting passwords, or via court order.
The attorney handling the probate might help you, or you can try the legal aids that work with that courthouse.
And as an aside, don’t forget to setup your own legacy contacts now and possibly get your parents to do it now. Having gone through this a couple times recently, it was very nice to have the legacy contact access. Made everything simple.