Sibling cards allow you to study cards in multiple display configurations.
By default, decks will present their cards according to how you configure the deck's Card Display setting. All cards will follow this configuration and look the same.
However, you may want to study information in multiple ways. If you're learning Spanish, for example, you might want to study by seeing the Spanish first, then the English first, and then by only being prompted with the audio. This is what sibling cards enable: a single card template can be used to create two or more actual cards, each being displayed in a different way.
In the sibling settings, you can add additional Card Displays in the order you would like them to appear. Cards will always be first displayed in the configuration set in the Card Display setting, followed by the configurations - in order - listed on the siblings screen.
Siblings are created at the moment you first add a new card to the main scheduling loop (by swiping it up or right). By default, sibling cards are scheduled ahead in 5 day increments so that the first sibling will appear 5 days after the original card, the second sibling will appear 10 days after, and so on. This value is customizable in the Algorithm settings as Sibling Lag.
This means that siblings will only be generated for new cards swiped after you add a sibling configuration. Siblings do not get generated retroactively for cards already in the main scheduling loop.
Sibling cards are completely distinct - your performance on or modification of any card does not affect its siblings.
CleverDeck doesn't allow siblings to appear in the same study session. If two or more siblings are scheduled for review during the same session, one of them will be rescheduled to the near future.
Siblings can be a very powerful and robust way to learn new information. However, it does effectively double or triple (or more) the number of cards that you'll have to review. If you ever regret your decision to add siblings, you can use the available option to just delete them all.