Zakaat

Calculating the value of gold for previous years' unpaid zakaat

Q: I wanted to ask some things related to the payment of zakaat. They are as follows: 

I was unaware that I had enough gold previously and now I have to pay zakaat for the last 2.5 years. So will the zakaat of each year be calculated according to the gold value in that year, or according to the current year's gold value? 

If I won't pay it all at once, and do it in installments will I be sinful in delaying it further?

Keeping money aside for sadaqah

Q: I have done a niyyat of giving money in sadaqah and that money is with me (waiting to find someone who is needy). If someone comes to me asking for a qarz (debt), can I give debt to that person from that money with niyyat that when he will return, I will give sadaqa of that amount (as it is ultimately sadaqa money) and if that person does not return money after a long period, I will assume that my sadaqah is fulfilled as I am not getting that money back.

Giving zakaat to one's brother in law

Q: Is my brother in law a recipient of zakaat? 

My sister and her husband have a few debts but at the same time they have a TV and phones and Alhamdulillah food in their home, water and electricity, and a nice home to live in even though it is on rent. 

We feel it will be incorrect to give zakaat to them because they are not termed under masakeen, poor or destitute but they do have debts to finish off.

My brother in law has recently opened his own business and slowly getting onto his feet.