Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
What is your current contact with your step mother like?
Was there anything in your father's will that restricted her entitlement to the property?
Have you any reason to fear that she has changed her will?
Have you discussed this with your brother and step sister?
What is your step mothers mental health like?
There is no legal action that you can take at this point.
Obviously the three of you should try and spend more time with her, and her own daughter should consider discussing Lasting Power of Attorney with her so that she can support
her with her finances if her mother's mental health deteriorates.
In the event that it does transpire that the Will has been changed then you will be able to challenge it on the basis of her sister's Undue Influence on her
I hope that this is of assistance - please ask if you need further details