How have the Van Daans, the Franks, and Mr. Dussel physically and mentally changed from the play's start to Act 2?

In the beginning of the play, everyone is healthy but very anxious about going into hiding. They fear for their lives each day, but they also have more hope and peace than other Jews because they have Miep, Mr. Kraler, and others to help them each day. Living in cramped quarters with seven other people, twenty-four hours a day for about a year and a half has a lot of side-effects, though. People get to know one another so well that pushing each other's buttons becomes very easy, for example. As food becomes less available, everyone's hunger increases as well. As a result, act 2 opens with Anne mentioning that everyone is "a little thinner," the Van Daans' arguments are worse than ever, and she and her mother still don't understand one another. 

The residents in hiding are also a little more desperate at the beginning of act 2 than they were in act 1. For example, Mr. Van Daan asks Miep to sell his wife's fur coat without asking permission. This is something he would never have done in act 1. Mr. Van Daan sells the coat mostly to buy cigarettes for himself, which doesn't make his wife appreciate him at all. Mr. Dussel has become more concerned with the size and distribution of food because he believes that Mrs. Van Daan always gives bigger portions to her husband. Hunger drives Dussel and Mr. Van Daan to be constantly worried about food and survival. The stage directions even say that Dussel is "disgruntled" with the way things are in the annex.

Therefore, most everyone hiding in the annex is stressed out, hungry, and easily irritated with one another. After being cooped up for nearly 18 months and struggling to survive the war on much less than they are used to, these feelings and physical afflictions seem to be quite normal under the circumstances. 

How did the Van Daans, the Franks, and Mr. Dussel change physically and emotionally by Act 2 in The Diary of Anne Frank?

When the play’s actions begins in Act 1, Scene 2, the new inhabitants of the annex of relatively healthy and relieved to be safe.  By Act 2, they are careworn, threadbare and thinner and fight amongst themselves.

Mr. Van Daan, “a tall, portly man in his late forties,” is smoking a cigarette, and his clothes are “expensive and well cut.”  His wife is described as “a pretty woman.”  Mr. Frank’s “movements are brisk, his manner confident” and Mrs. Frank is described as young.  Dussel arrives later, and he is “a man in his late fifties, meticulous, finicky.”

In Act 2, all of the people in the annex are shivering.  Anne notes that they “are all a little thinner” and they are definitely cautious.  They are also starting to get on one another’s nerves, arguing and fighting.

Although there are plenty of physical changes as everyone gets thinner and older, worn down from worry, the emotional changes are severe.  Anne notes that the Van Daans fight regularly, and the incident with the cake shows that everyone is touchy.  They are ready to accuse each other of things like not dividing food equally.  It is harder to have hope.