What comparison or contrast can be made with the challenge Santiago faces with him trying to catch the fish and the challenge Ray faces when his brother in law tries to take the farm away from him.

What an interesting question! Ray, the farmer, and Santiago, the fisherman, are both highly masculine characters who pull resources and their livelihood directly from the natural world—and of course, they both love baseball.
But more to the point, first of all, both are people with incredible tenacity and determination, struggling hard to hold onto something hugely important—something deeply meaningful. I would even go so far as to say that both Ray’s family farm and Santiago’s fish are like pieces of these men’s souls, that they’re central to these character’s sense of personal identity and meaning in life.
In Ray’s case, he’s struggling to hold onto his family farm, the place that fills him with pride and joy, a deeply important piece of land that connects him to both his family and the earth:

I don’t seem meant to farm, but I want to be close to this precious land, for Annie and me to be able to say, “This is ours.”

And in Santiago’s case, he’s struggling to hold onto the fish, a symbol of both his livelihood and his faith, a deeply important signifier of his remaining strength and resolution. Here’s Santiago as he muses, foreshadowing his encounter with the fish:

“I hope no fish will come along so great that he will prove us wrong…I may not be as strong as I think," the old man said. "But I know many tricks and I have resolution."

Second, both Ray and Santiago rely on their sense of intuition, placing their faith in superstition and signs from the beyond. Ray consistently believes in the truth and urgency of the voices he hears in his mind—“If you build it, he will come;” “Ease his pain.” And here’s Santiago, trying to catch the fish, relying on his superstition:

Then [the fish] will turn and swallow [the bait], he thought. He did not say that because he knew that if you said a good thing it might not happen.

Third, both men persist to the point of recklessness in pursuing their beloved goals (keeping the farm and catching the fish, respectively). Here’s Mark, explaining to Ray why it’s foolish to try to keep the farm:

“You’re going to have to face the facts,” Mark said to me.
“Your financial position is no secret. It appears to me that you either have to sell the farm now or lose it in the fall. Even if you have a bumper crop, which doesn’t appear likely, you’ll never be able to keep up with the mortgage payments. You can’t make a living off a quarter-section anymore. The days of the small farmer are gone forever.”

And here’s Santiago, persisting in his pursuit of the fish even as danger grows, even placing his bloody hands in the shark-infested water:

Now they have beaten me, he thought. I am too old to club sharks to death. But I will try it as long as I have the oars and the short club and the tiller. He put his hands in the water again to soak them.

So far, I’ve found similarities between the two characters and their struggles. Are there any contrasts? Sure.
On the surface: their situations are different, they live in different times and places, they have different reasons for holding onto their goals, Ray is young and Santiago is old, Ray has a family and Santiago has only his caring young friend.
Going a little deeper, we notice that Ray’s struggle requires intellect and luck, while Santiago’s struggle is much more physically demanding, even violent. And, although Ray’s victory is absolute—he gets to keep his farm in its pristine condition—Santiago’s victory is much more muted: he retains only the fish’s skeleton.