Raven

My Father recently passed away. He left a will in which he has left his 50% share of the house he owns with my Mother in a trust. The terms of the trust are that my mother has a lifetime interest in the house and can live there until she passes away, then my Fathers share held in Trust will pass to me and my two siblings. We (the Executors) are in the process of applying for probate, is it necessary to complete a IHT400 form or does spouse exemption apply? Thanks