As a lot of this I'm about to describe is a spoiler in some sort, I'm going to put this behind a cut.
One of the conventions that I will use is that "Good Wives" is actually the second part of the Little Women novel. The copy that I have has both of them in the same novel, with Good Wives being the second part.
Basically, this is information that is needed if you only watched the Little Women WMT anime and have not read the novel, as it only covers the first part and not the "Good Wives" part.
Jo and Fritz Bhaer
If you remember from Little Women, Josephine "Jo" March was basically the really headstrong sister of the March sisters. What happens in the second part of the novel is that she goes to work in a boarding school that was run by one of Mrs. March's friends. It is there that she met Friedrich Bhaer, who was a famous teacher in Germany, but was now a poor language instructor.
At that time, Jo was trying to make money from writing stories. However, the stories she were writing were not exactly "good" stories per se. Professor Bhaer saw a copy of the newspaper where Jo was writing her stories and told her that the newspaper was poison.
Basically, Jo held Professor Bhaer in high esteem, and what he said changed her forever. They also fell in love with each other, but neither knew the other's feelings.
After Jo returns home to her parents, Professor Bhaer comes down for a visit. It is there where he proposed to her in a muddy street in the middle of a heavy rainstorm. They were married a year later, and Aunt March bequeathed Plumfield to Jo.
Franz and Emil
They are Professor Bhaer's nephews. His principal reason for coming to the United States was to care for them.
John "Demi" Brooke and Daisy Brooke
The fraternal twins are John and Margaret Brooke's children. If you recall from the Little Women anime, we find out about Meg's feelings for John Brooke after the incident involving Laurie and the letter. In "Good Wives", Meg and John get married in the very first chapter. You will get to see them in episode 33.
Elizabeth "Beth" March
In the Little Women anime, she falls ill with scarlet fever after visiting a poor household. Unfortunately, she does not fully recover from it. She dies near the end of the second part of the Little Women novel at age 18. It is her death that is the catalyst for Jo to open her heart to Professor Bhaer.
You'll see a cameo of her in episode 34. If you recall from the Little Women anime, Amy March was the youngest of the four sisters. She eventually marries Laurie.