As a result, Ross is free to join Towergate in November, and the two others will make the move to Towergate in September.
The sum was part of a £20 million (US $30.9 million) settlement between Ross and the others and Gallagher. The remaining £12 million (US $18.5 million) was paid by Towergate's majority owner, Highbridge.
John Tiner, the former head of the Financial Services Authority who chairs Towergate, said: "I am very pleased that a settlement has been agreed between a number of incoming executives and Gallagher, bringing much needed clarity to the management of the Towergate business.
"With all of these appointments alongside our existing leaders we will have an outstanding executive team, whom I am confident will lead the business to sustained success in the future."
Privately owned Towergate originally announced Irishman Ross's appointment in February when it also unveiled a refinancing which led to big losses for investors.