Indeed, hope the last minute prep is going well for all.
At this stage we did do some days of 3 or 4 papers so that the experience of a whole day of testing wasn't too much. A bit grim, but balanced with lots of treats.
Unlike Lost, ds did have a preferred school. So we chose 2 other schools as back-ups, as much by looking at the test dates and ensuring that our preferred school was the middle date. We tried to avoid successive days of exams. From past experience I knew 2 schools would let dc sit as late candidates even after the main test day, and know of people who deliberately applied late and did get places and scholarships.
Ds stayed off school until the end of exams. Too many other pupils sitting the same exams, and I didn't want him facing the post-exam analysis.
Don't forget that the interviews are important. Definitely worth getting someone to do a mock interview. If only to remind dc that when asked what they do in their spare time, the answer can include cricket, cubs, choir, etc and simply be "watch television"
MGS papers are gruesome, but do have a lot of good problem questions which tend to appear at the end of maths papers.