All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If it is confirmed that your second elder brother is the one who bought the land and the six shops and paid their price from his own money and did not gift it or sell it to his father or to his brothers, and did not renounce them or part of them for his father or any of his brothers, then this land and the shops that it contained are his property and he has the full control over them and they are not part of the inheritance which his father left.
His elder brother has no right to act as he wishes about them on the pretext that he paid his father some money in order to build on it; because the father has no right to dispose of the money of his son unless he has a power of attorney in its regard from his son (the owner).
Even if the father has the right during his life to take from the money of his son for his need, the two following pre-conditions should be met as explained by Ibn Qudaamah :
1- He should not wrong the son by being unfair.
2- He should not take from his [son's] money and give it to another son.
The above pre-conditions are not met in the above case.
Therefore, the construction that the father or the eldest son did on the said land without prior permission from its owner is considered as extortion and it is not acceptable. Therefore, the owner of the land may demolish what was built on it or buy it as debris.
Ibn Qudaamah said: "If a person plants in other people's land without the permission of the owner, or builds on it without his permission, and after that the owner of the land asks to cut his cultivation or destroy his construction, the extorter is obliged to fulfil this, and there is no difference of opinion in this regard."
The crops of the land along with its six shops are a property of its owner, so its extorter is obliged to pay its price from the day he had unlawfully taken it until the day he hands it over.
As regards the money that the eldest brother had given to his father while he was still alive for the purpose of constructing on the land of his brother, then he has the right to ask for his right from the money of his father if he left any wealth, provided he had given this money to his father in a manner that is permissible. However, the money that the eldest brother had given to his father should not be an evidence or reason for disputing about the ownership of the property of his second brother.
Allaah Knows best.