Everything. For dying Frederick, that's what his children meant to him. Since his wife died with cancer decades ago, he chose to devote the rest of his life to their offsprings.
There's male #1, his too eccentric eldest son who still hadn't found a wife. There's male #2, a former junkie turned prodigal son. There's the only female, wooed by many men but too smart to not fall for gold diggers. And there's male #4, his Bible-loving youngest, who swore his loyalty to the church since losing his mother.
They were Frederick's everything but for them he was just money.