If I were George Milton in this story, I wouldn't have had the fantasy about buying a little shack with a few acres of land, and I wouldn't have encouraged Lennie to believe that such a thing was going to happen. George and Lennie have miserable lives as migrant farm workers, but they would be equally miserable living on such a farm. Having Candy along as a third partner would make things even worse. Candy could be of very little assistance with only one hand. If he did the cooking, the food would probably be pretty bad. George might be a better cook, but having to do the outside work plus a major part of the inside work would be insupportable.
The worst feature of such an enterprise would be that they would be "land poor," as subsistence farmers used to say. No matter how hard and how long they worked, all they could produce would be food. They would have no money at all. And that would mean that they would lack any of the little amenities they probably can enjoy as migrant workers. There would be no coffee, no tobacco, no alcohol, no sugar, not even any soap unless they could come up with some money. They could try selling some of the food they raised--but everybody in the area would be trying to raise a little cash money by selling vegetables, milk, and eggs. They would have no money to buy new clothes. Eventually all three men would look dirty and ragged. They would even stop shaving because they would not be motivated to care for their appearances, and anyway they could not afford to buy razor blades. They would probably have to cut each other's hair and do a poor job of it. They would have no entertainment and probably no visitors.
The only way they could get their hands on a significant amount of money would be to work as fruit pickers during the summer and early fall. That would mean following the crops, from apricots in early summer to grapes in the fall. But that would require a car or truck. Gas was cheap in those days, but it still cost money. Candy would be useless as a fruit-picker. And what if one of them got sick? Candy was old and would have been the most likely one to need medical care, if not hospitalization. Would George and Lennie want to be responsible for this old man with only one hand?
In a worst-case scenario, these three men would end up quarreling with each other. They would soon get sick and tired of their life of shabby clothing, a mostly vegetarian diet, an unpainted wooden cabin to live in, and nothing to do but work or sit around waiting for the crops to grow.
I don't know what I would do about Lennie if I were George. But I wouldn't accept Candy's money to help buy a tiny farm, and I would start giving serious consideration to finding a suitable institution for Lennie. The standard way for subsistence farmers to exist throughout America, as well as all over the world, is for a man to share a home with a woman. The woman can make life better by cooking good hot food and keeping everything clean and attractive. Typically they would have children, and the children could provide some purpose in their lives. Subsistence farmers had lots of children because it cost very little to feed them. George could earn money by working as a fruit picker, a handyman, and a part-time "hired man." In the meantime his wife would be there to look after their farm, look after the children, and feed the animals. As George, I would have no problem finding a wife if I owned a little farm. There were just as many poor women as poor men during the Great Depression, and the women had far fewer opportunities.
If I were George I would have to get rid of Lennie. He is too much of a burden, and he is becoming harder and harder to manage. George actually does get rid of Lennie in the end. No doubt he feels bad about it, especially because he had to kill him, but now at least he is free and has a chance to get a little happiness out of life. I might feel sorry for Candy too, but I wouldn't consider taking on an additional burden. It is always a mistake to take over other people's problems. The world is full of people with problems, and many of these people are more than willing to dump them on you.