This is not going to sound nice, but you and your husband need to get a backbone against that woman. She did not MAKE you get a DNA test. She did not MAKE you live in a two room hovel. You have chosen to allow her to bully you into those things. Your husband needs to say "mom, this is OUR home too, and I paid for it too, and I WILL reap the benefits of what MY money paid for." Then move into the house and tell her to go blow goats.
If you do sell that farm, I suggest you figure out how much income she has made from it (the guest house) and subtract half of that from any profit made, then split the profit. Do NOT buy her a new place, hand her the $$ and let her buy her own place. If you buy her a place, she will only find ways to make you miserable about it.
Seriously, man up and tell that lady to go suck an egg. Do it now, even if you are planning on moving. She has GOT to learn she cannot treat you that way or she will FOR THE REST OF YOUR LIVES!
I speak from experience. My MIL is a notorious liar and manipulator. Controlling and alcoholic. She has married five men and left them after she sucks their bank accounts clean, she has estranged many of her family, and she tries to guilt her sons into all kinds of things. My first experience (2 mos after starting to date my hubby) with her was we drove 8 hrs to see her for T-giving. When we arrived at my future bro-in laws for the day, she called and said since her sons didnt like her boyfriend she wasnt coming. SHE had said SHE would bring all the food. So, the boys were sad and prepared for spaghetti for dinner. I was enraged! I called her and told her was WAS going to get her a$$ over there and have thanksgiving with her sons, she hadnt seen my hubby for 3 yrs, she gets to see her boyfriend every day. She said she didnt have the food, I said then it looks like we are going to the grocery store. She came over, we shopped, we had dinner and she still doesnt really like me, but she respects me. That also allowed my husband to start stepping up to her and now she really doesnt try to pull much on us. She doesnt talk to us much either, but thats okay.