google sheets – How to match 2 cells for get a third cell

In the first sheet, I’ve in the row A the column of the users, I’ve in row B the column of the users and the column C the PC hostname of the users.
In the second sheet I’ve the firstname and lastname in 2 column A and B and the software installed.

How to match the firstname and the lastname for get the hostname where the software has been installed.

I tried a double Vlookup :

=IF(VLOOKUP(B2,'hostnameUSer'!A:D,4,FALSE) =(VLOOKUP(C2,'HostnameUser'!B:D,3,FALSE))))

I can not figure out