Thanks for your reply.
I've checked the help menu for "permissions" on Openledger, but it seems to only explain the overall concept but not the actual steps for setting up the multisig account. In fact, the example they used on the explanation seemed to exceed the total of 100% pie, so it simply confused me very much.
Do you know if there is a "proper" documentation on how to set up a multisig account/wallet?