In Italy, it is tradition to be named after your grandparents. Firstborn children are named after their paternal grandparents and second-born children are named after their maternal grandparents. This is more of a cultural tradition than a religious tradition, and may be common in multiple European countries.
Why do they have same baptismal name?
There is no biblical references for this custom within a family. It is simply a private tradition within some Catholic families.
This seems to be the case of some family tradition, perhaps due to a particular devotion to a particular saint within a family. It may also be a family tradition of some saint related to the ...