@Pumpkin
I have to read a litttle between the lines here.
First - I am assuming the transaction was between your beloved and his family.
Second if this had been a gift, then your husband was way above the threshold from Parent to child assuming it was a parent. That would mean a fairly substantial Capital Acquisitions Tax Bill. [So hold your horses!]
Third it may have been the intentions of the parties that they knew the implications of a gift and were treating it as a loan but didn't sort out paperwork.
Fourth this may or may not be secured on the house - it does not sound like it was.
Fifth assuming it was not secured, then under the Family Law Protection Act the non-owning spouse is protected in so far as the owning spouse cannot get a loan secured on the property without your consent.
So before you bring any house down establish the facts.
It may be that the Parent is elderly and has a truck load of assets and when they die your husband may be inheriting a bit more - sounds like he will unless the Parent alreday sold off the furniture etc - your get my gist?
So it may well be in your interests that this indeed is a loan - our erstwhile young buck that watches the Revenue @Mandletrot may suggest that if it were a gift, when did it happen and if it was some time ago your husband could have an issue on the lack of declaration of the Gift etc.
It may also be that the loan was given prior to you marrying your husband ..
so all in all we are still missing some crucual information - such as dates - your star sign and your volatility level
I think you now have a better base for a rational discussion with your beloved.
Does that help?