They actually just cleared this up in the recent update! One was named Blue and the other was named Gin, but Gin got taken by humans and was named Ao probably cause of his blueish/silver fur. So when the cats reclaimed him and brought him to their district now both brothers were named Blue.
Why are they named the same name?!???
Ao (青) means blue in japanese so their both named blue??!!?
Is this a little joke?? Or something