What is the ruling on stipulating that a debt be paid within two or three years, or else the entire land be owned, given that the debt was 30,0 Saudi Riyals and the current price of the land is 120,0 Saudi Riyals? And does this condition apply to all siblings, or only to those who were present at the agreement?

Do not destroy what you have built, and consider the circumstances of your brothers who are in hardship, as Allah says: "And if there is one in hardship, then grant him respite until ease." You are not allowed to sell the land or take it for yourself in exchange for your debt without their permission. If the debt is due and the debtor does not pay, it is permissible to sell the mortgaged item, return the excess over the original loan, and recover any deficit. The sale is handled by the Sharia judge or his representative after giving the mortgagor sufficient time as determined by the judge, unless the mortgagor authorizes the mortgagee to sell the collateral. If the land is sold, you are only entitled to the amount of the debt, and any surplus is shared among all.