Unfortunately, many of us have grown up in households where our parents' financial affairs were mostly unspoken. This is a generational blind spot that should be filled. This issue gets bigger when a parent passes away. If the other parent is still living, they may need to lean on you to help them with most of their affairs. If you have lost both of your parents and have not been informed of what they had and where, then you will spend ample amounts of your time trying to locate everything.
This checklist is meant for after-death use, but this is something you should be going over with your parents periodically. I understand there may be only one sibling that your parents trust to help with this sort of thing, and that is fine, but they need to get them involved ASAP.