Q: How likely would all 4 tires lose 8 pounds of pressure each at the same time when just a week before they were fine?

Tire pressure changes 1 PSI (up or down) for every 10 degree change in ambient temperature so temperature differences would not account for a large 8 PSI drop. The only other possibilities are leakage through the valve core and at the rim bead sealing area. For aluminum rims, if they are "old", you can easily lose 8 PSI due to corrosion. However, you seem to be indicating that this pressure loss has happened suddenly and thus, to this point, you have not had a problem with air leakage. I would say that if you are sure that there is no measurement error, and the rims and valve cores are all OK, then perhaps somebody reduced the pressure. If you want the rims and valve cores inspected for leaks, please use the tire rotation service request page as that inspection would be performed during tire rotation. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.