I mentioned my subjects in a different quote, but I did above average in all subjects except, IPT, Biology, Arabic and maybe 2 Unit Maths, but that was in year 11, it's gonna be a different story for Year 12.
Yeah ok. What I would say is:
-Try to see it from your parents point of view. If you can show them that you understand their opinion and have listened to them without interrupting, they are more likely to be open to negotiation
-it sounds like you did above average in chemistry then, while not above average is some of your others subjects, if this is going to change in year 12 that's fine but my advice would be drop the subject you are least passionate about. If you really enjoy Chem then the time won't be that bad because it's not that much of an issue if you are passionate about it. But if you don't really enjoy it then you need to tell your parents that by doing subjects you enjoy more you will be much more likely to do better as spending the time and effort studying will seem easier to you
-also tell your parents that the scaling doesn't make that that much of a difference (except for like gm vs m. ex2 ) so if you got mark x in subject a, that would be better then getting a much lower mark of y in subject b. Head to an ATAR calculator and play around with this, use specific examples
-Also from your below average grades in your other subjects, while you do say things are going to change in year 12 and they will it can be hard for your parents to believe that so you may need to say this is what I want to change and this is how I will do it...
-With me, I convinced my parents I should drop SDD while I was rank 1 in it in order to bring up my english mark in it through having that detailed knowledge of atar/scaling/units/raw marks/importance of balance etc. which helped significantly and using specific examples of how marks would compare using an ATAR calculator as well as percentiles and how easy it would be for me to get certain marks. I also emphasised that all the time throughout the whole entire year I spent on SDD could be spent on English, which is heaps of time
-If nothing is working, speak to your school 'careers adviser' if you have one or even teachers and get them to talk to your parents about it
Hope this helps!