Good stuff, could it be that Sherman's were in the process of making a decision to stop funding an organization, and in desperation that organization decided to have a meeting with the Shermans and 'make them an offer'? It seems very far fetched that a 'charity' would operate in this way. However maybe an individual(s) from the 'charity' decided on their own to take rogue action? Could it be that somebody was embezzling from a charity, and the loss of funding from the Shermans would result in the scam being discovered?
The charities to which the Shermans gave large donations were all large, well-known and reputable. This seems like a highly unlikely motive.