Review the following links
Crude oil lasts hundreds of millions of years underground, but is gasoline at risk of spoiling?
www.livescience.com
87 octane fuels tend to be less refined and contain more unstable hydrocarbons. As the months pass during storage these unstable components react to form gums, varnishes and lower octane hydrocarbons. As a result the octane can decrease within months for 87 octane fuels, especially when stored under less than ideal conditions. 93 octane fuels are more refined and contain more stable hydrocarbons. These stable hydrocarbons can last 2-3 times longer than 87 octane fuel. Even in proper storage 87 octane gas can start to degrade in 3 months, 93 octane fuel should last closer to 9 months before degradation is noticeable. Keep in mind that 93 octane fuels are still susceptible to octane loss and vapor pressure decreases due to butane evaporation.
https://www.sunocoracefuels.com/tech-article/octane-stability-high-octane-vs-low-octane-fuels
If you have 87 octane in the vehicles, a bit of Startron or Stabil will at least allow you to stop caring about it.
Having said that,let say you do nothing and the cars sit for 6 months.
At that point, you MAY deal with a bit of reduced performance as the knock sensor does its thing. It all goes away at the first refill.
In other words.....
If you car is just going to be sitting for just a couple of months, you need it for piece of mind more than you car needs it.
You car will be fine at the first refill.
What would I do?
Depends on the vehicle.
Trackday or motorcycle.? Probably.
Everything else? meh.