What is the ruling on utilizing the father's share of the inheritance land, which has not been legally divided, by investing in it such as planting trees and building tents for raising chickens, with the approval of all heirs?

As long as the land has not been divided, all heirs are partners in it according to their inheritance shares, and it is not permissible for anyone to exploit a part of it by building or planting except with the consent of the other heirs. Whoever does so without permission is considered an usurper and is obligated to remove what they have introduced, because every part of the land is shared among them. Therefore, if the heirs permit you to exploit the land, it is permissible for you; otherwise, it is not.