Blades boss Neil Warnock had arranged the signings of the duo last week but had to wait until international clearance had been granted.
Shelton has signed a contract until 2010 and joins from Swedish outfit Helsingborgs at a cost of £1,850,000. Meanwhile Fathi, who also signed a deal until 2010 cost just £700,000 from Egyptian club Ismaily.
With Sheffield United out of the FA Cup the duo will have to wait until next Tuesday (30 January) to possibly make their debuts when Fulham travel to Bramall Lane.