Hey! Former year 12 student here. I did practically the same subjects as you so I might be able to give a bit of information to help you make a decision.
In terms of HHD, unit 3 content does have a bit of overlap from 1/2. Rest assured, if you were to start in 3/4 directly, all of the prior content is reviewed (in a lot of detail if your teacher is good, otherwise textbook questions are great for practice cause it’s simple stuff). The only content you will need to know is health and wellbeing, health status, nutrition, and Australia’s health system.
So, if you’re worried about lack of knowledge for HHD, it’s actually not so bad. You can catch up in no time. Now, is HHD easy though? I would say it’s easier conceptually than other subjects (e.g. specialist) but that means that a lot of people do well in it. To score highly in it, you’ll need to do a lot of practice (esp. Cause it scales lower). Nevertheless, it was my favourite and highest scoring subject in VCE so it’s possible for you to do well without your score scaling down.
English, though, can be a double-edged sword. Because you do literature, practising writing more essays is definitely a plus. While assessments and ways of thinking are quite different in both subjects, you can still benefit by building vocabulary, writing speed (helpful in the exam!) along with the general quality of your written expression. It’s also beneficial because if you do poorly in Literature, you have a back up. English is always in your top four so if scoring high is your priority, english is the safer option. But the workload for both can be challenging to manage. Reading so many texts and writing essays is a huge time sucker.
So overall, viewing both HHD and English from an effort less can be helpful but if you’re aiming for higher scores, it’s better to consider interest. If you’re passionate about a subject, you’ll naturally do more work for it and then score better. Have a good think about where your interests lie. I hope that you can make the best choice for yourself. Good luck for Year 12!