The phrase "about their willingness" is correct and usable in written English.
It can be used when discussing someone's readiness or openness to do something.
Example: "The manager expressed concerns about their willingness to adapt to the new changes in the workplace."
Alternatives: "regarding their readiness" or "concerning their openness".
Democrats are sending more mixed signals about their willingness to negotiate.
I've talked to Democrats about their willingness to work with us in Congress.
Republicans have certainly been disingenuous about their willingness to provide resources for diplomatic missions.
"I can confirm that we received signals about their willingness and readiness to discuss this issue with us," he said.
Today, many of Egypt's top TV presenters and journalists are remarkably candid about their willingness to act as government mouthpieces.
Government officials have been particularly blunt about their willingness to see housing prices decline somewhat, to make homes affordable to more of the nation's 1.3 billion people.
Turkish diplomats sought to reach a negotiated solution in Libya, but complain that Libyan officials lied to them about their willingness to impose a cease-fire.
"We are very excited about their willingness to engage in dialogue, take actions and become an active participant in creating a less hostile atmosphere at Madison Square Garden".
They have made various cryptic statements over the last six months about their willingness to offload loss-making papers that they see no prospect of turning into profit.
Mr. Harvey said he was surprised that the executives were so open about their willingness to manage their businesses to meet Wall Street's expectations.
It suggested a formal meeting could have been held to discuss directly the worries that health professionals had about their willingness to accept guidance.
