Legal Charge on Property

After a bit of advice on this one. Quite complicated and involves a couple of subjects. To summarise I bought a restaurant business back in 2006 which involved the business and a freehold property.the original sum was quite a few hundred thousand for which we received a loan from Abbey Commercial and to make up the shortfall we took an 80k loan from the vendor. The loan was secured as a charge on my partners fathers house for a 30k portion and on a house in London which was jointly owned by my Dad and Aunty for 50k.We have paid over 30k off so far leaving a balance of 48k with no defaults or problems.
Now it gets complicated!! My dad is very seriously ill and trying to get his affairs in order. His will leaves his half of this house to myself, my brother and my sister but it is clearly going to get very complicated. The main question I have is can we keep the charge in place by simply getting written agreement from the original loanee and transfer my dads half of the property now, to myself and my two siblings.So can changes basically be made to the ownership of the property with the charge still in place. Any suggestions as to the best solution, we have two properties, but neither have more than 25k_30k equity so a transfer may prove difficult. Apologies if not quite the right forum, but any experiences, help etc would be very much appreciated.