data validation and function

[edsarrabis]

A	B	C	D	E	F
First Name		LastName		Middle Name

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guys please help me on this,
in Cells B1, D1, F1 , i will use data validation for the drop down list, however,

if I will choose one last name, its first name and middle name should be changed automatically, i am using vlookup here.

what if it has the same last name?how will I get the correct first and middle name? what function will i use? thanks

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