who are twill and bonnie, and what news do they share with katniss?

Twill and Bonnie have escaped District 8, where there has been an uprising. Twill was a teacher, and Bonnie was a student.

Ever since the Hunger Games, the discontent in District 8 had been growing. It was always there, of course, to some degree. But what differed was that talk was no longer sufficient, and the idea of taking action went from a wish to a reality. The textile factories that service Panem are loud with machinery, and the din also allowed word to pass safely, a pair of lips close to an ear, words unnoticed, unchecked. Twill taught at school, Bonnie was one of her pupils, and when the final bell had rung, both of them spent a four-hour shift at the factory that specialized in the Peacekeeper uniforms. It took months for Bonnie, who worked in the chilly inspection dock, to secure the two uniforms, a boot here, a pair of pants there. They were intended for Twill and her husband because it was understood that, once the uprising began, it would be crucial to get word of it out beyond District 8 if it were to spread and be successful.