Settlement clauses are valid or void

Testatrix had executed a valid registered Will making A beneficiary of her one-third share in the house property. After testatrix died A filed a probate petition. B is willing to give a no objection to the said registered Will. I of my own due to my love and affection for you, I say - 1. that whenever full house is sold A will make 4% extra payment to B of value of one third share in the house property allotted to him long time back in partition of the said house. 2.That B will not go for specific performance and demand for selling the house. 3. It is made clear that 4 % to be given as mentioned above if full house is ever sold as aforesaid mentioned does not mean that B will have ownership rights in Testatrix shares in the house. I do not want to sell the house,can B file a application in court that A is not selling the house and not giving my 4%. I want to know whether the above clauses are valid