do I move sixth forms for yr 13

i am currently in yr 12 and go to an independent school on a 75% bursary. i'm happy and quite settled since ive been there since my gcses and my teachers like me and i do quite well - i've been selected for a prefects role for yr 13 next year.
the only problem is that recently, the school moved down my bursary from 75% to 50%, starting from next year. this is quite a significant jump and my parents aren't really happy about this. it's very unlikely my current school will give me anything more than 50% as it was originally 25% and after much arguing with my parents, they only moved it up to 50%. i wouldn't have stayed at my current school for sixth form if they didn't give me the bursary and it's annoying because it's tricky to move now.
my parents want me to move because if i stay at my private school for sixth form with the 50% bursary, it will use up all their savings which means they can't use the money to do some construction work that they wanted to do on our house because some of it is old and falling apart. and also, my sister is 99% sure she is moving to a grammar for sixth form and my parents thought it would be good for me to move to a grammar to set her up, so she isn't going somewhere completely foreign to her.
there are two grammar schools that my parents are thinking of sending me to, and she's emailed to check and they're willing to offer me a place as long as i work hard. but there are a couple downsides:
grammar A only offers 3 of the a-levels I am taking: i am taking bio, chem, music and psych, and they don't offer psychology so i would have to drop it, and i don't know if i could handle starting an epq in yr 13
grammar B offers all 4 but all 4 subjects are different exam boards whereas if I went to grammar A, one of the three subjects i'd take is the same exam board so more catchup work for grammar B.
i'd imagine id have to do a lot of catchup work over the summer but this will be extremely difficult as i'm planning to do medicine and i have to revise for the ucat, i have a 3-week summer camp that is compulsory, and also i have my piano diploma exam as well as writing my ucas application i believe.
i'd also have to get used to being in a new school, new friends, new environment etc.
basically the negatives are a lot of hard work but there are positives as well:
obviously the reduced cost + being able to set up my sister
both grammars have around 10+ oxbridge students every year, i really want to do medicine at cambridge so this will be really beneficial, as we only have around 1-2 oxbridge students at my private school every year
both are also very academic with lots of medicine students - often i feel like teachers at my school try to discourage students from taking medicine and they don't offer as much support
also other notes of consideration: i know people at both schools so i won't be completely alone, i'm academic and the type of person who works hard when they encounter a difficult situation, i'd probably be adjusted by the end of yr 13 but it would take a pretty big mental toll, and it would take me a long time to adjust, i'd have no leadership roles if i went to either school.
i feel really conflicted and would love to hear from other people - maybe some people who moved schools for yr 13?
ty x
edit: also, i am currently at a girls only school and my parents would prefer it to stay it that way - grammar A is mixed and grammar B is girls only
update: there's a third grammar school, again not offering me psychology, but two out of three subjects are the same exam board. but there's a lot of controversial stuff surrounding this grammar. it's quite small and it's very very academic and also quite competitive. the travelling time would be the longest around 45mins to 1hr. over 20 oxbridge acceptees