This.
My wife and I have dealt with all 4 of our parents passing away, and the one thing that is certain is that as soon as the bank/brokerage/whatever knows that the primary account holder is dead, they go hypervigilant. Either have the various accounts and safety deposit boxes in joint ownership, with rights of survivorship, or have unambiguous beneficiaries set for all for your/their accounts.
The courts can take months or years to get things straightened out, but if you need the money to keep paying the mortgage on their house you may not have that much time.
One last thing, make sure that they have given Medical Power of Attorney and Full Power of Attorney to one(!) trusted child / friend while they are still legally competent to do so! Almost worse than losing your parents altogether is watching a 6-way train wreck happen as people begin fighting over the spoils ... before there are any spoils to fight over.
It can get ugly. Be prepared.