Hey Highway_end,
Welcome to ATAR Notes! 
You should be able to do four in Year 12. I know that some schools are a little hesitant, though. My only thought here is the lack of continuity with your subjects (like, the year between Bio 1/2 and Bio 3/4, Methods 1/2 and Methods 3/4 etc.). I'm honestly not sure if that would be an issue or not, though. 
I'd almost be inclined to do Bio 3/4 next year, but that probably depends on a lot of factors.
What are you hoping to do after Year 12 at the moment?
Hi, thank you for the reply!
After Year 12 I plan on doing Medicine in uni, keeping in mind the difficulty and high ATAR required

My school doesn't allow us to do Bio 3/4 or Methods 3/4 in year 10.
Instead, we have to do Spesh 1/2 in year 10 to fill the gap, but can choose to drop it later on (ie. not do Spesh 3/4 in year 12) which is what I'm doing because maths isn't my strength and I don't enjoy doing it lol
I have found out at school today that we MUST do 5 subjects in year 12 even if that means taking a 3/4 without a 1/2. Something about the curriculum being designed like that and how if we have too many free periods, students tend to slack off and get lazy (kinda stupid imo)
Any advice on which 3/4 subject I should do without a corresponding 1/2??