This is the 358th most frequent Arabic word.
أنهم
"أنهم" means "that they" in English.
The word 'أنهم' here combines 'أن' (indicating a statement) with 'هم' (referring to 'they'), introducing a statement attributed to someone else.
قال لي صديقي أنهم قد وصلوا إلى الحفل.
My friend told me that they had arrived at the party.
In this context, 'أنهم' is used with 'أظن' (I think) to embed the thought, linking the idea of 'they being ready' as the clause's subject.
أظن أنهم سيكونون مستعدين للاجتماع.
I think that they will be ready for the meeting.
Here, 'أنهم' conveys the sense of 'that they' following 'من الواضح' (It is clear), connecting the introductory statement about their dedication.