Carer got free accommodation but also paid for all utilities and groceries bills. I would call that about even. (They get free accommodation but didn't have full freedom in the accommodation, and paid bills).
on the caring front. I don't know actual costs or hours the sibling was available. But imo it is probably worth min 12k per month. And likely more like 20. So rather than low balling offers id prefer to see min 50-80 coming off the total inheritance of the other siblings.
I see that as the minimum.
if the parent was difficult, even more
if nobody else wanted to do it even more
if they had good earning potential even more.
The person presumably did benefit from a closer relationship with their parent, and hopefully good memories and bonding and insight into life. But given the alternative costs and it being strangers I feel like 50-80 is the minimum deserved.
Is careers allowance about 250p.w.?
I accept it might be very hard and full of friction to come agreement on that though.