Probate - Property Held in Trust

[Steve19]

My wife and I are executors of her mother's will. Her mother is widow, and near the end of life. My wife's older brother (who has never married) still lives with his mother. The will states that the house should be held in trust for the use of the brother for as long as he wishes to continue living there. When he dies, or decides to live somewhere else, the proceeds from the sale of the property should be divided equally between all surviving siblings. My question is: should the value of the house be included when determining whether probate will be required? Also, if the value of the house plus other assets is above the inheritance tax threshold, will the tax have to be paid when my mother-in-law dies or only when the property is sold?

[Elsie2021]

Following on from above question
If the property passes to the trust at the point of the mother death but cannot sold until the brother either dies or decide to vacate
When does the capital gain tax start?
Does start at the point of the mothers death?
Will the surviving sibling have to pay capital gains tax on the increase in house valuation from the valuation at the mothers death to the valuation at the point sale (which may be many years later)?