Hi! I did the summer school last year, my subjects were Biology and Chemistry. You'll be absolutely fine. They are definitely university style lectures and you do them in real lecture rooms. It started off really basic like N5 level (energy shells, how to balance an equation) then got up to Higher level later. It's kinda handy to be refreshed on important parts of the periodic table like electronegativity, electron affinity and atomic radius though, it came in handy in my lectures this year. You'll need to take notes so take a notebook or laptop with you.
You do get tested (I dug out my old notes and saw I got 2 assignments given in week 1) like in real uni but these tests are pretty easy if you've been paying attention. Nevertheless you'll need to set aside a couple hours a week to complete these like in real uni. There's also an exam at the end of the summer school which I sailed through but do make sure to attend every day of the summer school to make sure you pass it.
For us in science the lecturers were new to teaching, so like PhD students or graduate teaching assistants, so some were good lecturers and others not as clear at explaining things. But you can ask them questions at the end and you get course contacts you can email.
Make sure to wear enclosed shoes for the labs and full length trousers, hair tied back, they won't let you in if you're not wearing correct kit (really).
Chemistry lab is not very good at explaining things, so ask other students for help. (It's not just you) The labs are really fun though so try to go to them in person because otherwise you'll be doing digital 'virtual labs' which kinda suck (in my opinion)
Most importantly - don't forget about the 'academic skills' module you'll be given to do (it's in every subject not just science). It's very easy but takes an absolute age to do because you have to click between different pages. Start it early and get it out of the way so you don't miss the deadline.
With commute distance, you're best emailing the summer school email about that.