What is the reason that we as a community do not hear about the other daughters of Rasulallah? Additionally, if he knew what Uthman would become why would he let two of his daughters marry him?

The reason is that we don’t believe the Holy prophet had more than one daughter. According to our tradition, he had only one daughter ( Bibi Fatema (as))
The other daughters according to our tradition were the Children of khala ( Bibi Khadija’s Sister).
They came to stay with the holy prophet the lost their mother.