Unfortunately because you have been paying and have acknowleged the debt (albeit a smaller one than they originally asked for), the debt is not statute barred and therefore the short answer is yes, they can put a charging order on your new home.(posted 7847 days ago)However, this does not necessarily mean you will be dispossessed, it means that when you sell the house, you will have to settle both the mortgage and the charge.
As for declaring the repossession in 1991, it depends on what the new mortgagees asked you - if you were asked if you have EVER been the subject of a repossession and you answered no, then you could have committed an offence, but it is unlikely your new mortgagees will ever get to know or if they did, pursue it so long as you are paying them what they owe you.
As a thought - if the charging order is made, your new mortgagees will be made aware of it, but not what it is for.