@friendassistance , I have gone back and refreshed my memory about US-Italy tax treaty. From rereading your posts and responses from my colleagues , what I get of the situation is as follows:
(1) your parents acquired a real-estate in the year XXXX for equivalent to US$AAAA. This asset was jointly held and thus your mother had 50% and your father had 50% ( if the whole ;prop was US$100,000 then each had a basis of US$50,000)
(2) Once your mother passed , your share of the asset amounted to US$BBBB , allowing for FMV step up of your mother's share of the property and recognizing your sibling's shares -- let's call it US$FMV1. ( Thus if you had two other siblings and the FMV of the house was US$200,000, then the basis of the property of your share would be US$100,000--- your mother's share stepped up by 1/2 FMV----- divided by three i.e. US$33,,000
(3) when your father passed again we have a step up of his half . So if the FMV of the whole property is US300,000 , then his basis of original US$50,000 gets step-up to US150,000. This means each of you siblings' share of this half becomes US$50,000. Thus your basis on the total property is now US$33,000 plus US$50,000 = US$83,000.
(4) Thus when you dispose of the property at FMV --- US$300,000, each of you three siblings ( for US purposes ) have a gain of US$17,000
Does this make sense ?
Is there more I can do for you ?
pk
