Is agricultural land registered in the name of the deceased mother considered property belonging to all heirs, including the father, or to the father alone? And does the son who cares for his ailing father have the right to claim his share of the profits from this land and other properties of the father? And do the other siblings have the right to claim their share of those profits, especially if they have not received anything from them for years?

It appears that your father registered the land in your mother's name for a temporary reason, not as a gift. Therefore, the land remains his property, and no one has the right to dispose of it or take any of its profits without his permission. Neither you nor your siblings have a share in it as long as your father is alive, for the living do not inherit. Whoever among the children works on the land is entitled to the profits as agreed upon with his father; if no agreement was made, then he is entitled to the wage for his labor.