Re your last post OP
The executor is wrong
If one beneficiary can be found but others cannot, the executor or administrator must take ‘reasonable steps to locate the individual’
before finalising the estate.
The administration cannot be delayed indefinitely, but directly distributing the missing persons' shares to the found beneficiary without legal protection can make the executor personally liable for the missing amount
You need to put this in writing to both the solicitor and executor.
Basically
Once exhaustive searches have been completed without success, ( several methods and worth googling OP )
the executor has several options to proceed, often involving legal advice:
1/ The estate pays a premium for a policy that covers the cost if the missing beneficiary reappears later.
2/ A court order is obtained that allows the estate to be distributed on the presumption that the missing beneficiary has died. This protects the executor
3/ The found beneficiary receives their share but signs a legally binding agreement to repay the funds if the missing beneficiary is found.
4/ The share of the missing beneficiary is set aside in a trust or special account, allowing the rest of the estate to be distributed.
5/ If other options are not viable, the funds can be paid into the Court Funds Office