Get a caveat lodged today. See this link for form 4:-
http://niprobate.info/ (I do not think there is a charge - download the form, fill it in and hand deliver it to the nearest probate registry and it will be effective from tomorrow).
Then write to the aunts, explaining that you have lodged a caveat since under the bit of legislation I quoted to you (also quote the case law, that is going to be equally as valid in NI), the previous will was not revoked and the estate passes under that will. Point out that they have no title to the property or the goods and you will immediately seek injunctive relief for which you will seek to make them personally liable for the costs. (In fairness, this letter ought to really come from the executor of the unrevoked will). Send this recorded delivery. Unfortunately, that may well have the effect of spurring them onwards, so if they are not actually doing anything right now (easy just to drive past the house), it may be best left until you can get formal legal advice.
It may be worth phoning a few solicitors - some will have an emergency number during the festive season. Round here a lot are open today, tomorrow and Wed.