How do the number inscribed on the relative arm create an eerie atmosphere during the family dinner?

The number on Aunt Eva's arm is well known to Hannah. It is the same number that was on Fayge's arm in the camp. This reveals that Fayge and Aunt Eva are the same person. Aunt Eva changed her name when she came to America.

The number on Aunt Eva's arm is familar to Hannah because it shows that Aunt Eva is actually Rivka. When Hannah traveled back to the Holocaust, she took the form of Chaya, who later died in the end, saving Rivka's life because Chaya make Rivka switch places with her and telling Rivka to run away. Rivka changed her name to Aunt Eva, so no one would recognize her.