If you can share important details like passwords of bank account or safe, or grant them access to important documents, should we not also be able to trust these people with access to our bitcoin wallet?
You should let them know, but it isn't necessary, IMO, to share access to the keys, just as you do not share the same wallet or bank account. But, sure, let them know you're holding x coins, for example. If you're together, that means you trust each other.
I'd hesitate sharing access not because of secrecy, but incompetence. If you both stack sats, go for it.