They allege that Mr Sanea abused their trust, concealing his borrowings from them and forging documents bearing the signature of Sulaiman al-Gosaibi, one of the founders of the group.
Al-Sanea has made most of his fortune investing in construction and finance, particularly by securing contracting deals for the construction of residential and industrial buildings near Saudi Arabia's Al-Khobar region.
As boss of TIBC, Mr Stewart says he took instructions from Mr Sanea because he believed that the Gosaibis had given Mr Sanea full power of attorney to act on their behalf.