'expressed their willingness' is correct and usable in written English.
You can use it when referring to someone's readiness or eagerness to take on something. For example: The board members expressed their willingness to take on the challenge of finding a new CEO.
When these appellees applied for their jobs, they expressed their willingness to take such oaths.
"There are one or two who have expressed their willingness to provide some troops," he added.
M&S, Carphone Warehouse and BDO becoming founding partners, and many more have expressed their willingness to be involved.
Other families expressed their willingness not only to be interviewed but also to be advocates within their communities.
However, these four conservatives expressed their willingness to support changes with Paul explicitly stating he was "open to negotiations".
During the phone call, the four alternatively expressed their willingness to die for their cause and their openness to surrender.
The French favored Italy as trustee for all the colonies, and at the April session the Soviets expressed their willingness to accept the French proposal.
The situation in Haiti remains dire, and the Aristides have expressed their willingness to help Haiti rebuild, through education initiatives and in other desperately needed areas.
The Bosnian Muslim officers were arrested on Thursday by federation police officers, and today they expressed their willingness to surrender voluntarily to the tribunal, a government statement said.
We designed a Choice Experiment where landowners expressed their willingness to accept afforestation contracts with varying attributes, one of them being the likelihood of being monitored.
After the new council met, officials expressed their willingness to be flexible to build trust and pave the way for direct negotiations.
