Estate procedure

My father who had remarried since the death of my mother from cancer unexpectedly passed away. His wife has dementia and was in and out of the hospital. I was always assured that the house he built with my mother was going to me (his only living heir) - - but where his wife is still alive her daughters have come up from Texas to Maine and say they have a buyer for the house and are taking it away from me. The will did not specify that I was to receive the house if his wife survivied me... But she has dementia as well... The daughters moved her to another state and seem to be taking everything from me...... I dont know what to do.