MS-Excel: License on Web Server

[bvasanth123]

Hi,
I have a web intranet application where user exports xls file. The web
app takes that xls file and parse the xls file using office object in
VB.NET.
1) If all end users have MS-OFFICE liences on their devices, should I
need to buy separate license for installation on the server (IIS)
2) If end users do NOT have MS-OFFICE liences on their devices, should
I need to buy separate license for each end user + 1 for the server
(IIS)
3) If it is internet application, what is the licensing model to buy?

Regards,
Vasanth