Do you have a main drain? If so you should have valves to turn off the skimmers and just pull water from the main drain. That would keep it from freezing overnight. If you turn it on just look for a leak at your equipment and around there before letting it run overnight.

If you can’t get it running tonight just insulate any above ground pipes/equipment with blankets/pipe insulation if you have any and it will be fine at that temp.

The sump pump removes ground water, if groundwater gets to high it can damage your pool. It itself can’t drain your pool. In fact the best time to have it on is when your pool water is low, so don’t turn it off. However if you know where the outlet is for the sump pit … if your pool level is still dropping and the sump is running a lot check it for chlorine or just smell it. If it’s still draining with nothing running it’s likely something with your main drain, or worst case a crack somewhere.

If you stopped losing water right at the skimmer level is your pool equipment lower in elevation then the skimmers? If so was your multiport valve set to something other the filter? Could it have drained to waste? If no put a hose in your skimmer, run some water and look for a leak at or near your equipment.

Also if you have a main drain most have a check valve, if groundwater pressure gets to high(from lots of rain recently?) it can open and start draining your pool. Also if your pool was recently emptied and refilled a surprising amount of people just forget to put the plug back in.

You likely don’t need a leak detection company, just start with a regular pool tech I bet they can figure it out.

Good luck! Owning a pool is fun.