I remember your last thread OP. You were very stoical, but I remember being upset on your behalf that your brother got the money and your parents only told you right at the end.
I’m a solicitor, but not in your jurisdiction. But here you can have something in the will saying “I give [insert amount] to DC1.”
If you want the amount adjusted for CPI/inflation, you can include:
“The amount referred to in paragraph XX is to be adjusted for inflation from the date of this will to the date of my death according to the movement of the CPI between those two dates.”
However, we don’t have inheritance tax here, so you would need advice as to whether this impacts that.
You should also ask your parents, what is their plan if one parent passes first, does that gift come out of the first will, or are they mirror wills where it’s all left to the other partner, and the gift comes from the second will?
Finally, what if there is no money left - IHT or care home fees or just spending. What do they propose to do then to ensure the money is fair?
I’m encouraged that they are actively trying to put it right, and I would strongly encourage you to work with them to get wording and an outcome you are happy with. If you do so, hopefully you can move past the favourtism and hurt feelings from before (and despite what people are saying, I read the other thread and you are 100% right to feel this way!) and start to enjoy your relationship with your parents and brother again. I fully appreciate what a kick it must have been last time.
I think you should also share with your parents how this made you feel, as it their minds, they thought/knew they were going to be ‘fair’ later, so it was fine. But you knew nothing of the sort, and whilst it’s nice to assume families all ‘play fair’ after a death and can work it out between themselves, my profession shows me every day that is ain’t so.