I am sorry for your situation but impressed with your priorities - kids and wife - first. Can you advertise the horses - offering a free lease - someone may be interested and at least they can do all of the work and use them at your property until you sell them and perhaps whoever does this may want to buy them eventually. This will free up your time a bit and take the load off of your family. How much work has to be done? When I had health issues a few years back, my wife organized a work day, my brother, his good friend and 2 my of my close friends came and gave me 10-12 hours of their day to finish projects around the property - ie: round pin, fencing, firewood etc... with a BBQ at the end of the day. They all wondered when the next work day was being scheduled... they had a blast. Perhaps you could make a list and see if any TBNers live close by and or gather some people from your church and close friends and go at it... with a big feast afterwards.
I would finish the fencing and buildings - they will add value to your property for resale.
""At the moment, if I plan to stay married (which I do) at a minimum the horses MUST go, & she is refusing to let me finish the pasture fence and run-in shed (too bad for me that I've already bought the lumber and gates), and the plan is officially we MUST sell Mossflower Woods as soon as we can get our money back, maybe even before that..."" - - - Sounds like this may buy you some time.
Not sure I can offer any suggestions on the counselling side - others have made good suggestions for you both - hopefully your wife will be open to things.
Hang in there... there will be better times.