There isn't a flaw in the conditional logic here. If all marsupials do not lay eggs, and at least some marsupials are native to Australia, then it follows that some animals native to Australia do not lay eggs:

mars → /eggs (A → /B)
mars ←s→ Australia (A -m→ C)
______
Australia ←s→ /eggs. (C ←s→ /B)

This is a valid conclusion taking the form C ←s→ /B. We're looking for an invalid conclusion that says B ←s→ /C.

This parallels our stimulus:

(Franz says) father → /want children eat candy (A → /B)
father -m→ adult (A -m→ C)
______
want children eat candy ←s→ /adults (B ←s→ /C)

The legitimate conclusion would be "some adults do not want their children to eat candy at bedtime" (adult ←s→ /want children eat candy). This answer choice instead concludes a "contrapositive" of that statement: some people who want children to eat candy at bedtime are children (/adults). This is the same pattern as in the stimulus.

This is a different flaw than what we're looking for. It runs:

(Yuri says) metal → /equal to best oak (A → /B)
California -m→ metal (C -m→ A)
______
California → /equal to best French oak (C → /D)

Notice the flaws here. From Yuri's premises, we could reach the conclusion that most California wine is not equal to the best wine aged in oak (California -m→ /equal to best oak). But instead Yuri reaches a conclusion about all California wine, somehow comparing it to the best French wine aged in oak. We know nothing about how good French wine is, compared to the best wine aged in oak in general. This is flawed, but a different pattern than we're looking for.

No flaw in the conditional logic. If all color film produces images less sharp than the best black-and-white film, and most instant film is in color, then it follows that at least some (in fact, most) instant film must produce images less sharp than the best black-and-white film.

(Xi says) color → /as sharp than bw (A → /B)
instant -m→ color (C -m→ A)
______
instant -m→ /as sharp than bw (C -m→ /B)

This is a valid argument.

Wrong flaw. Notice how the argument runs:

(Betty says) corp → /like pay taxes (A → /B)
corp -m→ honest (A -m→ C)
______
like to pay taxes ←s→ honest (B ←s→ C)

From Betty's premises, we could legitimately conclude that some honest people do not like to pay taxes (C ←s→ /B: honest ←s→ /like to pay taxes). A flawed conclusion following the same lines as the stimulus would be that some people who like to pay taxes are not honest (B ←s→ /C: like pay taxes ←s→ /honest). But this answer choice somehow reaches a conclusion about people who both like to pay taxes and are honest, which is not supported, but a different flaw from what we're looking for.