1- Technically it would be permissible for you to deduct the outstanding debt from your Zakah calculation but since this is a long term debt, thus you should not deduct it from Zakah calculation. It should be treated as no asset or liability. You should calculate your Zakah on the remaining assets that are in your possession including cash, gold, silver etc...
2- Zakah will become obligatory on your retirement fund once it reaches maturity. Once it reaches maturity then you would be required to give Zakah on the entire balance.
3- Since your daughters have passed the age of puberty, therefore if the gold and silver that is owned by your daughters reaches the minimum Nisaab then they would be required to give Zakah. If it does not reach the minimum Nisaab then no Zakah will be required.
4- If the land was purchased only for the purpose of sale then it would be treated as a business inventory, thus you would pay Zakah on its wholesale value. If it was purchased with any other intention then no Zakah will be necessary.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America