Welcome to the frozen club. It's -8 here this morning and no issues with anything including my diesel because up here in Michigan, it is always treated with Power Service white bottle, buggy's batteries are topped off and replaced when a few years old as well as the tractors and the SxS as well as my diesel pickup are on battery tenders and my AF coolant was checked or renewed this last summer. I always check my AF concentration with a Brix Refractometer. Inexpensive and accurate tool on Amazon, good investment as it not only checks AF but electrolyte charge level in flooded cell batteries and coolant concentrations in my flood cooled machine tools. The one I have set me back less than 15 bucks. Checked both tractors last night and the fuel bowls on the Racor's were perfectly translucent and no cloudiness at all.
I'm sure with a little bit of glo-plug action, both would pop right off, no issue. Starting batteries are also fully charged and out of circuit with master disconnect switches. Something that is SOP with me as they sit for long periods of time unused and master disconnects insure the starting batteries don't suffer discharge from any parasitic loss. Flooded cell starting batteries lose about 5% of their total charge per month of not being used and a full charged flooded cell battery is good (remains viable) to about 30 below zero (f). Discharged batteries will freeze and become useless at much higher temps, BTW. I break them out to insure they will crank the cold engines when required. Cold engines require substantial more amps to turn over and start. Finally, I always install the largest group size and cold cranking amp batteries that will fit physically, in the battery trays, always. In the case of my M9's, Group 31 with 1200 CCA. My batteries get load tested every year with a carbon pile load tester and when they start to degrade, they get replaced and that includes the vehicles as well.
Harbor Fright has a nice carbon pile load tester pretty cheap I might add. Handy tool to have.