Wife discharging zakaat on her gold for previous years

Q: I have been married around 15 years, and my wife was give more gold ornaments by their parents! There is zakaat to be given for it and she did not provide it! I don't have any gold or savings! Only my wife's gold! How can I calculate the zakaat for the past 15 years => Gold price was low to high till now. Do I need to calculate the yearly gold rate on that year! Can tell me how to discharge the zakaat for the past years?

Distributing the land in inheritance when one heir built a structure on it

Q: I built on my mother's property with her permission, my sibling doesn't want to compensate me for the improvements. She say that I occupied it for free for many years. 

My Mother is late. I have one sibling (sister) we and are heirs to the property. 

What is the Islamic ruling on this? Does she have a claim on the building that I erected with my funds and the proceeds that come from it or does she have a claim only for the land that the building was erected on?

Performing salaah on a plane while sitting

Q: A person read salaah on the plane. Due to severe turbulence and short time for asr and the flight crew not allowing him to stand, the asr Salaah was read sitting on the seat not facing qiblah. 

I understand that one will have to repeat this salaah standing up afterwards. The time of asr ended and maghrib time came in. The flight now landed. 

1. Will the Asr Salaah be regarded as invalid and Qadha have to be read (fardh not done at all), or was it a valid adaa but necessary (waajib) to repeat the salah? 

2. If one is saahib e tarteeb and the next salaah comes (e.g. maghrib comes in), will one read the next salaah (maghrib) first, or repeat the salah in question (asr) first? 

3. If someone in the family did not have wudhu, and neither had anything to make tayammum with, then performed the Asr Salaah sitting on the seat in that state, will the masla change in both questions 1 and 2?