Did Meg and Charles parents understand them?

Well, Mr. Wallace doesn't really come into play before Meg rescues him, but the children look up to their father and miss him. Mrs. Murray's references to her husband are filled with love.

As a scientist, Mrs. Wallace is also a fantastic parent, and yes, she does understand her children. Mrs. Wallace well understands that her behavior will influence the behavior of her children, therefore, she's very careful to control her emotions around them. Meg envies this, but she also sees how difficult it is because of her parent's relationship. Two years is a long time to keep your chin up.

The following excerpt about the family comes from the study guide available here on gradesaver;

The Love of Family

L'Engle's stories often are meditations on the nature of love, and in A Wrinkle in Time, L'Engle chiefly focuses on the nature of love between a family. Meg's own life is thrown into turmoil over the fact that her father has left and not contacted them in a year, and from the beginning of the novel her troubles are often related to this absence in her life. Mrs. Murry and Charles Wallace are also deeply affected by this loss in their own way.

Though it is sad, L'Engle reminds the reader that it is this bond between family members that helps to give the children the strength they need on their journey. The novel also shows how this love can bring others into their family, such as with Calvin. Calvin's family is contrasted with the love between the Murry family. Calvin's own home life is in disarray, and when he meets the Murrys he feels as though he has finally found where he belongs. Thus, the love shared between families not only gives Meg and Charles Wallace the strength they need, but it gives Calvin the motivation that he needs as well. The Murry family is, thus, shown to have entered a sacred bond different than that of romantic or brotherly love.