Resign - accept that something undesirable cannot be avoided.
Dad resigned to his seat. "Fine," he says.
Relent - cease resistance.
Dad sits back in his seat and relents. "Fine," he says.
Capitulate - cease to resist an opponent or an unwelcome demand.
Dad sits back in his seat, capitulated. "Fine," he says.
Acquiesce - accept something reluctantly but without protest.
Dad sits back in his seat and acquiesces. "Fine," he says.