My Dad put his home in his and my sisters name when he had cancer 15 yrs agoas he was dying. At the time the tax appraisal value was 200,00. She was to get the house and i was to get the equal amount in money. The appraisal now is over 400,000. He expressed many times that he was sorry he did that as now there is not cash to equal 1/2 of that amount. He gave express instructions to my sister ( now the executer of his will)and to me that she would now have to pay the difference so we both end up with equal amounts or assets.
Do we use a tax assessed value or a real estate appraisal now to assess what is half?

What can i do to help get my equal share?