what happens when if an institution gives a morgage on a house where someone else has a quick claim on the house?

When my mother died I inherited a house which I quick claimed to a niece who then signed a quick claim to my brother as it was intended to be his but since his daughter would be living in it he wanted to make sure of tax benefits on living in the home...She somehow got a mortgage on the house without his permission which he was furious about...so much so that he cut off all with his daughter...she even moved out of the the house but kept up the mortgage and taxes, but told him he would be responsible for the large mortgage she took out if he excersised the claim, which he couldn't afford unles he sold ,which he didn't want to do, as he was hoping it would be his old age security blanket...He passed away due to the stress of the estrangement from his daughter..he revised his will and trust and everything he owned was left to me...How can she sell the house as I have paper "quick claim deed" from her to him...Shouldn't this cloud the title? She and her mother a both lawyers so they do the intimidation routine and think of things to try to circumvent the law...She is trying to sell the house now Which I found out about because I was checking the value of the property on websites such as zillow...What are our rights? Hers? the house is in california...