ANSWER:

A man is not obliged to be fair when he marries another woman and gives her a mahr! 

So if she demands a house or a property and he writes that to her, the first wife doesn’t have the right to demand a similar property.

QUESTION: my father gave my mother ( his 2nd wife ) a property before he married her as a gift because of wish of my maternal grandfather cuz my grandfather had trust issues with my father. The gift was a in a sense collateral if things went wrong (like my father leaving my mother etc ). When the gift was given, he was not married to my mother. They were totally non mehram. Does my father should also g