Thanks for the additional information
Can you advise under what conditions that HMRC state that the money is owed back?
I am afraid the NIL statement does not in itself negate the overpayment position, It just means at the time the year was signed off, that it was beleived nothing was owed either way, but clarly there has been an issue since this time, and it may have everything to do with the leving the UK.
This is because if he family moved abroadm, then they only would have continuted to qualify for tax credits for 8 weks following the departure date. But you advise that this relates to more than 5 years ago and they have only lived abroad for just undr 3 years, so it cannot be for this. so could you advise further.
The property coulod be at risk I am sorry to say, but much is dependent on
1) Whether any payments towards this are going to be made
2) Whether the overpayment HMRC state arises is correct
3) The age - which I dd not realise this was a 5 year old issue
But until I know how this arose I cannot really comment further