Is it true that Imam Hussain offered prayers behind Marwan without Taqaya and that this is mentioned in Wasail al-Shia?
This is untrue.
Infallible never prays behind a sinner. Such narrations are fabricated even if you find them in a book compiled by a Shia author. This narration is mentioned in Nawaadir Al-Raawandi, page 30 but it has no value nor any authenticity.
Wassalam.