u/Maleficent-Ad-5063

Here is my wild theory for where the series will go next season

It will show infant Oona with her mom who is a young teenager on the island. She meets Steven and Goldie and they talk about how cute Oona is and how sad they are they can’t have kids of their own. Weeks later, Oona’s mom discovers she’s pregnant and later finds out they are twins. She gives birth and directs the adoption agency to make sure Steven and Goldie have the chance to adopt the twins.

Therefore, Oona is the sister of Annie and Conner.