What are the differences in character and behaviour between Sophie's mother and David's mother in The Chrysalids?

The first thing that strikes us about Sophie's mother,
Mrs. Wender, who is a more sympathetic character than David’s mother, is that she is
very much on her guard and suspicious. She answers the door when David approaches her
house with what he as the narrator describes as an "anxious abruptness." He says she
looked at him "sharply and frowned" at him.

The next thing
is complicated because three traits are bound into one reaction. Firstly, after David's
explanation of Sophie's accident, Mrs. Wender's reaction is directed toward Sophie's
injury, "Oh!... Her foot!" There be a hidden double meaning yo this since Mrs. Wender
knows that it a six-toed foot. Secondly, she suspends her concern for "a moment" to look
"hard" at David while she evaluates David's trustworthiness. Thirdly, she makes a
decision about the inevitability of trusting David to take her injured child, and says,
"Where is she?"

Through the remainder of the two scenes
involving Mrs. Wender and Sophie (at the rock and back at the house), she shows tender
love for Sophie. This is especially evident when she kisses Sophie's mutated foot that
could condemn her to the realm of non-humanity:

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[David] watched her mother pause to look down at
[her foot] for a still moment, lift it, bend to kiss it gently, and then look up with
tears in her eyes.

She also
shows tender acceptance of David and courageous trust in him regarding the fearsome they
now share, the secret of Sophie’s six mutated toes.

David's
mother is a diametrical opposite of Mrs. Wender. David remarks that his mother has a
"damping manner of listening only to correct," which strongly suggests she lacks the
tenderness Mrs. Wender displays. This is confirmed in her treatment of Aunt Harriet
after her abominable suggestion that their babies be switched for the purpose of
attaining a certificate that authenticates humanity by confirming normalcy as defined by
the Definition of Man.

David compares Harriet to his mother
and says he see in her a “little softened version" of his mother. She shows a lack of
compassion when she imperviously demands to see Harriet's baby without the wrapping of
blankets, calls the baby a “Monster!” and has Joseph order then both out of the
house:

My
mother said coldly, forcibly: "Harriet, let me see that child--properly. … Tell her to
leave the house--and take that with
her."

Harriet describes what
they see as "a little thing." David suspects it might be a sixth toe like Sophie’s
[Though there is no clue, I agree based on one of David's earlier remarks that parallel
the “little thing” description: "It seemed a very small toe to cause such a degree of
anxiety."] These cold hard traits are mitigated a little when she cries for what seems
to be a deeply suppressed secret sorrow after Joseph reminds her "that you yourself have
had to make your own penances twice!" This seems to allude to two births of baby's with
mutations.