Thank you Tallulah, we have had a family member in a similar situation. The course chosen was a it of a mix - it involved keeping a formal track of loan repayments, with the final amount to be taken out of the inheritance.
However, I would say that the estate was under the inheritance tax threshold, and did not involve such a large amount. But if you are interested, this is how it worked:
Let us say 3 children, A B & C, all to inherit equally once both parents are dead. Say estate is £200k actually owned by parents at time of death.
A owes £100k under the arrangement described. They nominally 'repay' the estate, to make it back to its 'real' value: £300k. It is then distributed: £100k to each child. A gets nothing at that point.
The serious drawback here is if your estate is likely not to allow such a distribution, so that A would owe their siblings, but might be unable to pay them. Depending on the amounts involved, that might be a risk worth taking.