If they had opted for continuous exam conditions assessments, they would have been inundated with equally angry parents furious that their children were being put under inhumane levels of pressure when they hadn't even completed the course and that not enough time was being dedicated to mental wellbeing.
If they stick with a single batch of exam condition assessments, they would have complaints about how it's inhumane to put so much pressure on them by assessing purely on the basis of a single day.
If they hold assessments in classrooms, they would have complaints about how it's inhumane to assess them when there is no room/somebody with a cough or a sniff/there is noise in the corridor or above them.
Somebody will complain the tests were too hard and it's not fair or humane.
Somebody will complain the tests were too easy and it's not fair or humane.
Somebody will complain that there weren't any tests and it's not fair or humane.
Somebody will complain that there is any form of assessment taking into account work completed in lockdown.
Somebody will complain that the assessments aren't taking into account work completed in lockdown.
Somebody will complain that there was an expectation to do any work in lockdown.
Somebody will complain that there weren't punishments for failing to complete work in lockdown and there wasn't enough work being given.
Somebody will always say at [other school] they aren't doing anything at all and are giving the kids vastly inflated grades for free.
In short, whatever way you look at it or do assessments, there will be people furious that the way that is chosen as to be the best for the kids to maximise their results fairly. Because they don't think their child will be the one benefitting from that particular approach, whatever it is.