Set Fullname up as a calculated Attribute, using your own formula
Note that the underlying structure of Mendix is rather tolerant concerning data-redundancy, and the calculated attribute is bad(ish) for performance reasons..... so, the better solution is to crate an "on commit" MF to (re)set the Fullname.
This could get you going, without storing the full name: Use a non persistent entity for this, with an attribute for concatenating the name parts and link this to the Employee objects. Then when selecting the non persistent object retrieve the employee.
Alternatively, you could use a Text widget - see screenshot below. This will not work in a datagrid, but should work in all other scenarios: