Hi @Robin1370,
To my understanding if you created the listing and created it as a separate entity and not with your current listings(I see 3) then there should be no problem. It would be like having your own and separate account.
If you added the listing to your profile than no, they would not have their own separate login and password. You have to build them their own profile etc. Perhaps have them as a cohost if you are managing for them or visa/versa or was this a consult on setting up a listing for them?
Bettye6