Mali international Sidibe arrives at Hillsborough on a 28-day emergency loan deal and is available for selection against Leicester on Saturday.
Sidibe has scored 26 goals in 186 appearances for Tony Pulis' side but is yet to feature for them this season.
Left-back Helan has joined Wednesday on loan until 22 December and is also available for the visit of Leicester.
Helan has been involved with the Manchester City academy for the past three seasons and made his first team debut in the 4-2 home defeat to Aston Villa in the Capital One Cup this season.
The former France U19 international has previously spent time on loan at Carlisle and Shrewsbury and now boosts manager Dave Jones options at Hillsborough.