The fact is that the trust exists, and cannot just be ignored because it is “convenient” to do so.
The fact that the original paperwork is missing does not invalidate the trust. It is fortunate that copies are available - consideration might be given to the clients making a statutory declaration in respect of the missing documents, confirming that the copies are “true” copies of the originals.
If the copy trust deed(s) include powers to wind up the trust and distribute the property to the settlors, then that route could be adopted, although there will be tax considerations. An alternative is to apply to court for the trust to be set aside if it is considered to have been “mis-sold” i.e. entered into under a mistake. Whilst liabilities would arise, payable either out of the trust or by the clients, it may be possible to claim reimbursement against the company if it carried PII.
Are your clients the trustees, or is the trustee the company now in administration or an associate of it?
If the clients are the trustees, they can control what happens, going forward. If not, and the trustees are unwilling, or unable, to cooperate, it may also be necessary to apply to court for the appointment of replacement trustees.
In any event, sounds like the clients need to make new wills ASAP giving a life interest in a half share of such property as they might own, rather than specifying a particular property.