Disowning Family Members

My best friend and her husband had agreed to buy his father's house after he passed, for market price. This would have kept it in the family and kept prop taxes at prop 13 levels (1500-2k/yr) She sold her current house, to buy deceased FIL's house.
Husband sisters insisted they were being cheated, it was worth more, voided the sale, and demanded it was put on the market.
Best friend was forced to buy a different house.
Best friends FIL's house finally sold...... for LESS than my friend and husband had agreed to pay.
Sisters lost a couple thousand dollars each, thru greed.
My best friend pays $6000 in prop taxes, EVERY YEAR, as a direct result of her husbands' sisters greed. So, underwater in a house that has to have been refinanced twice, and out an extra $45,000 in prop taxes.....so far.
Best friends husband hasn't spoken or had contact with his sisters in years.