Hi Molly - I am sorry to read of your loss.
Our online guidance explains what's required depending on the specific circumstances re the title being registered and in whose name -
HMLR Guide: Start - External · HM Land Registry
If you answer the series of Qs and remain unsure then feel free to post again but provide some specifics re title number and I can try and assist further
I'd also add that whilst I understand the desire to save money on legal fees it is often advisable to at least get legal/financial advice that transferring the ownership into your joint names is the 'best' thing to do for all, especially if you intend to buy your own homes later for example
Land registration is complex, designed to protect legal and financial interests in property. There can be significant consequences for any error. Please consider seeking legal representation. Before making an application without legal representation, it is important to
consider the benefits of using a conveyancer.