GFplux I disagree profoundly with your comment on not using %s in a will, and your reasoning for saying so. I saw a house brought to total dereliction by someone leaving his much younger second wife a fixed amount of the value of the family holiday home.
Between making his will and dying, the testators holiday home rocketted in value, by the time he died the fixed amount he had left his wife had gone from half the value of the house to barely 10%. So she refused to agree to the sale. The children lived in Australia, so they did not visit it or use it, neither did his wife and over 20 years we watched a very pretty thatched cottage seaside home become totally derelict. The roof collapsed and the forest around Sleeping Beauty's castle was nothing to the state of the garden.
When the second wife died, the plot was sold and the collapsed remains of the house demolished.
If a family want a fight over a will, they will fight regardless of how carefully the will is drafted.
I would, and have left money to our grandchildren that dousen't come from the money left to DS. It doesn't have to be a large sum. Say, your estate is worth the average value of a house at the moment, roughly £285,000. If you have three children, one with 3 children, to leave the grandchildren £5 - £10,000 will make very little difference to how much each of the adult children will inherit.
We are in that situation, except that it is 2 children and 2 grandchildren. However, in our case, our DD has told us, without any kind of prompting, that she considers that any money or support we give to our grandchildren is entirely separate from anything we give to her and her brother.
We have also left small sums to our niece, godchildren and a substantial amount to charity. Our children know all this.