LGIreland

I am looking for some advice. My mother in law died and left her house to her and her two sisters. They applied for probate and then sold the house. They never lived in it and from our understanding the deeds were never changed to be in their names (throughout the probate and execution of the will process). Doing some research online it looks like she had a "legal interest" in the property. Does this mean she has had a major interest in the property and therefore is not eligible for FTB Relief? Solicitor and mortgage advisor say we should be fine but to get a guarantee in writing we will need to pay a tax specialist around £600. We are likely to pay this amount to find out for sure but wanted to find out some more before we choose to do so. TIA