Hey I currently am a year 12 student at xaverian and i do biology, eng lit, politics and an EPQ. Personally in my experience, xaverians biology teachers are not that good and i never had the best time in my classes for bio either but it is AQA biology so thats up to you. I had a brilliant time in the rest of my classes xaverian is honestly an arts college and hence the sciences aren't taught as well here as humanities. My brother went loreto and hes in medical school now so i do think loreto is more of an science college. But likewise if you want to do sciences you will be pressured by either colleges to do well. I would say aqa biology is much easier in terms of resources but the teaching at xav for bio is not the best at least from my experience its more of a powerpoint karaoke. If you do go xaverian and end up with a bad biology teacher, ill not name drop but....youll be pleased to know teachers for bio change in y13
the way bio is taught is you get a green booklet for notes and qs for each topic, there are 8 booklets in y12
epq is taught really well and its much more relaxing, i cant speak for geography but id probably advise you to do a much more easier 3rd a level since if ur interested in med/dentistry they dont care what your third subject is
if you do end up going to xaverian then let me know, id be happy to share my y12 notes for bio
in terms of making friends everyone is super friendly and youll be fine
hope you enjoy your summer break and if you have any more qs let me know, i also think it would be much better if you heard from someone who does all 3 sciences