I didn't know you could give people money in your will conditionally, i.e., that they give nothing to the WTS. I thought once they gained control of their inheritance, the decision was theirs unless it was a trust and the money was doled out by a third party such as a bank or a guardian or attorney.
Remember, too that some states in the US have laws preventing a person from totally disinherting their children or spouse. In light of that it would be good to have a good attorney help you draft your will. Be candid about what your utlimate goal is, making sure the WTS doesn't get a penny.
Mulan, has a point too, many people before they die, give their family part of their inheritance, family heirlooms and cash.
Consider giving your money to charities whose ideals you support, especially if family/friends really don't need your money.
In the end, I figure a person's money is theirs to do with what they want even if it is misguided. After years of having my parents try and control me emotionally by disinherting me and reinstating me in the will every time I didn't lock step behind them, I finally just emotionally divorced myself from the idea that I would ever get a penny or want a penny from them.
Blondie (who has a will)