"their steadfast" is a perfectly correct phrase in written English.
You can use it to refer to a person or group's unwavering commitment or adherence to something. For example, "The team showed their steadfast determination to achieve the goal."
Mr. Cheney added that their "steadfast charade had raised the bar for all future Administrations".
If anything, their steadfast belief in Mormonism made them more rock'n'roll.
Americans think of Tony Blair, their steadfast wartime ally, as a prime minister guided by his convictions.
The financial crisis and subsequent government bailouts prompted some American policy makers to wonder if their steadfast belief in minimal state intervention had run its course.
Their steadfast riffs leave room for genuinely volatile singing, and for an audience that spread well beyond the This Tent, Ms. Howard was ready to belt.
"I would like to thank my family, friends and my employer for their steadfast concern and support," he said in a statement released on Saturday morning.
While the Joint List includes a number of disparate groups, ranging from Communist to Islamic parties, they are unified in their resolve to remain on their land and steadfast in their struggle to fight for their rights.
Trapped in Camberwick Black, their disarmingly steadfast relationship served as a surprisingly tender counterpoint to the snowballing unpleasantness of their new life.
The songs moved at their own steadfast pace, unhurried and adamant.
Through it all, McCain, their silent steadfast accuser, remained the same.
Since 2003, when the U.S. destroyed the Iraqi state and began spending billions of dollars trying to build a new one, the Kurds have been their most steadfast ally.
