How have the Van Daans, the Franks, and Mr. Dussel changed physically and mentally from the start of the play to the beginning of 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.