Are you clear that no IHT is payable when one half of a married couple passes away, and leave his/her estate to the spouse? Any IHT is payable only when the second partner dies, and it is payable on the residual value of the estate, less any nil rate band allowance. Also the nil rate band from the first to die is transferable to the estate of the second to die, meaning that the value of the nil rate band is currently £650k.
In any event (no deaths in the short term), creating a limited company that establishes you and your wife as directors may be beneficial, but you really need proper (paid for) tax advice on this.