Hi @MMarian,
Welcome to the Bunnings Workshop community, and thank you for your question.
Unfortunately, I wouldn't class this as something you could repair yourself.
Due to the load-bearing nature of your balcony, rusted materials pose a significant risk that could weaken or even cause failure of the deck. The rust on the outside bearer is of particular concern as this is directly supporting the rest of the deck through its attachment to the posts.
I would hate to give you advice that only covers up a bigger issue.
I would suggest you speak with a structural engineer for their assessment and recommendations for repair.
I'm sorry I can't be more help.
Jacob
