Using a password manager’s emergency access feature to access and transfer money out of a financial account when you do not have the legal authority to do so does not strike me as wise. If the individual dies you could lose many legal protections. In the case of death it’s not just about “trusting siblings” - there could be creditors who now can make a claim against that amount.
If parents want to achieve the end goal you describe there are thoughtful ways to go about that that don’t involve fraud, such as the aforementioned joint account or POD.
My point is that while this feature is great to gain access to important information. Those with emergency access should be very thoughtful about using the access to masquerade as the account holder.