Transfer of Ownership to Family Member – Tax exemptions?

My family moved into our PPOR 20 years ago, the house has been owned by my grandmother for over 50 years, my mother and father moved in after my grandfather passed away and they carried out large extensions to the property and have since taken care of maintenance and paying the bills, etc. whilst my grandmother remained on the residence in a “granny flat.” However ownership has never been transferred from my grandmother to my parents and they are now trying to figure out the best way to transfer the ownership that would avoid stamp duty and any other applicable taxes.

Would any special consideration be given to our case?

P.S. I am a property student so don’t be afraid to get technical.

Thanks.