If I were to cast Hijack onto something then were to cast Rescue onto it, would I then be able to play it as my own creature, or would I even be able to cast it on the creature? I feel like if it were the former someone would have played this earlier, can someone explain what would happen please?
Rescue explicitly says "..its owner's hand". You are the controller since you took control of it, but the owner of a card never changes; your opponent is still the owner and Rescue will put the card in their hand.
You can *never* have cards in your hand, library, or graveyard that you do not own (that is, that did not start the game in your library).
You can *never* have cards in your hand, library, or graveyard that you do not own (that is, that did not start the game in your library).