If it is important to you and you'd be happier there then go for it. Also **** your uncle, he cites THE
https://www.timeshighereducation.com/world-university-rankings/2017/world-ranking#!/page/0/length/25/locations/GB/sort_by/rank/sort_order/asc/cols/stats (times higher education, which is not the same as times university guide) as one of the best guides (I agree it probably is, but even that isn't/should be seen as gold standard, all guides have a huge element of BS in them, THE is just seems less BS than the others, QS is another good one), well Bristol is a top 100 (71) in that guide, maybe he is jealous or something. Seriously, just **** people who will put you down like that man.
I've literally no idea about Oxbridge selection processes, that door was closed to me long before I took my GCSEs so it isn't something I've looked into. Someone else on this site will know, there are lots of Oxbridge applicants/students here.
To answer your question about foreign universities, you'll find the majority of courses at decent overseas universities these days tend to be in English or will at least have international programmes. When you think about it, say Thailand for example, teaching only in Thai limits their student population to Thai speakers, offering English courses opens the doors to many more students given English is essentially a universal language. Across Europe, France, Germany, Netherlands etc will offer English courses, same for HK, Singapore, Japan, China, Korea, etc it just depends on who willing you are to go overseas, it is obviously more hassle in organising visas, flights, finance etc, in the UK it is a matter of a UCAS application and an SFE application, then you're done.