I don't think they should sound alike, just confusing.
But I don't mind a theme, for twins or other siblings.
Hannah and
Grace are fine b/c they could be names of sister who are not twins.
"But it’s all right now.
I learned my lesson well.
You see you can’t please everyone
So you got to please yourself."
Rick Nelson,
Garden Party
"It does not become me to make myself smaller than I am." (
Edith Södergran 1891-1923)