A subject access request ie..the legal framework under which they have to give you the information. It is time consuming for them so much better for them to just give the grades. They can however only give rankings if it does not specifically identify other pupils so for small cohorts it won't be available.
Appeal deadline is 17 September
Exam entry (A level) is 4 September but we are saying end of August about school for internal deadline. We still don't know what the fees will be.
I think just start off with a friendly approach along the lines of so we can consider worth sitting can you let us know did the final grade match what was submitted or has it been subject to moderation. If moderated you may think this is an easier decision as to whether to resit. If it matched maybe a conversation about whether realistically sitting would bring it up. Remember they keep the better of the two grades. Remember also that unis are supposed to be looking at results leniently when deciding places.
You/your DC may be happy to just move on if they miss what they wanted (ignore grade levels required) but still have their uni place.