Is it permissible for two sisters to sleep in the same room, each on a separate, individual, and opposing bed, during fasting, while being able to see each other?

There is no harm in a man sleeping with his sister in the same room on two separate beds, provided each of them covers their 'awrah (private parts) and takes precautions against exposure. There is no difference in this between the state of fasting and other times. As for the details of the 'awrah: a woman's 'awrah for her brother and maharim (unmarriageable kin) is everything except what usually appears. A man's 'awrah for her is what is between the navel and the knee.

The purpose of separating children in their beds after the age of ten is for each of them to have an independent bed, or for them not to sleep unclothed on one bed. Each of them must take precautions when sleeping, wearing what covers their 'awrah and protects them from exposure.