All members of your shared account are able to top-up and transact with that account only. They won't be able to access any of your accounts or private info. Ever.
You also won't be able to share your account with anyone who isn't on the Spot app and part of having an active Spot account, is being FICA verified.
BUT, you still need to know who you're sharing your account with because the responsibility of managing it is all yours.