Yes, you for sure need to get and carry a can of Quick start(ether) in BOTH vehicles
When temps are that low its hard for gasoline to be vaporized, and a spark plug can ONLY ignite gasoline VAPOR
Ether has a much lower vapor point so spark plug can ignite it, and that gets cylinders hot enough to hopefully vaporize some of the incoming liquid gasoline
Depending on the engine lay out, you just need an Intake vacuum hose to spray the ether into
Power brake booster is often easy to access and its a direct shot into the intake, pull it off spray in the ether, put it back on, the engine will suck it in when you crank
The PCV Breather hose is also another place, its often on the oil filler tube and runs to the air plenum from air cleaner
You spray ether into the air plenum, not the oil filler
But it is on the outside of the throttle plate, so spray in the ether then push down on gas pedal a bit to suck it in when cranking, there would be a delay before it fires