I'd do the one furthest downstream, if that were an issue.

Also, you can get a cheapo droplight and a chicken coop warmer bulb from Home Depot or Tractor Supply that'll keep pipes from freezing.

Lamp: https://www.acehardware.com/departments/lighting-and-electrical/work-and-shop-lights/portable-lights/3810645

Bulb: https://www.homedepot.com/p/Feit-Electric-BR40-250-Watt-120-Volt-Incandescent-Red-Heat-Lamp-Light-Bulb-250R40-10/304312180

Obviously not great to run all the time, but if a few of these keep your pipes (especially near the walls with outdoor spigots) from blowing up, then it's still 10x cheaper than a plumber. We used to use a few of these in the house I grew up in. It was an old 1800 granite block foundation that let all the cold air and flooding brook water pass through, so the pipes were tested every February, and this helped.