I am not qualified to advise, but, based on my experience, it could go on for years.
Yes the Solicitors should invest the money, but with interest rates as they are, and the estate must pay tax on the interest, it won’t be a lot.
The bit that worries me is the phrase, I am the appointed administrator. Does this mean that you personally were named as the administrator of the estate, not just that your permission was obtained for some other body to administer the estate.
if so then you are personally liable for any errors that may occur, I hope you have a solicitor acting for you personally.
Every known beneficiary has to be traced, if they are known but cannot be traced then their share must be held against a future claim.
Legal expenses will consume a significant amount, so don’t hold your breath
Mike
Mike