Setting up a trust to receive death benefits

A deceased was a member of a pension scheme which is due to pay out a death benefit of around £300,000. The member was under 75 and the pension was not in drawdown. The pension trustees have decided that they will only pay the benefit into a discretionary trust which will pay an income for an older sibling for the remainder of her life (currently in a residential placement) and then the default beneficiaries will be other family members. The deceased did not establish a pilot / bypass trust (or otherwise) during their lifetime for this purpose. Am I correct to assume that the deceased’s personal representatives can establish the trust on behalf of the deceased? If so, I assume that this would not affect the IHT position of the estate.