YES and NO, depending on what you want to achieve with the sharing of your cards!
YES - You can share your cards or rather restore all your cards on a second device. There is a feature in Stocard that allows you to transfer cards and other information to a second mobile device - the Stocard Backup.
To find it, please go to your settings in Stocard and choose "Backup". Then you can sign in with either Facebook, Google+ or your e-mail address. As soon as you are logged in, you can choose the option to create a backup.
On your second device (or your partner's device), again go to your Stocard settings and choose Cloud/Stocard Backup again. As a next step, sing in with the same details you used before. This time, choose the option to restore backup. All your cards and information should be automatically uploaded onto the second device.
NO - However, if by sharing you rather mean synchronizing two or more devices then the answer has to be no. After you restored the backup on your partner's device, there is no synchronization between the two devices (although the same account was used to restore the cards). That means for example when you add a card on one of your devices, it will not be automatically transferred onto your second device.
The examples above were both for scenarios in which you only have one Stocard Backup account. You can also have two different accounts (e.g. yours and your partner's), manually add the same card(s) and show the same card(s) at checkout.