Does the "Fruit of the Poisonous Tree" extend as far as this:

from LawVol
If the answer to the first question suggests no legal basis for holding the wife, then everything that happens after is tainted by that fact.
....
from Ken
Given no legal basis for custody of the wife or kids, all that follows would be illegal.
and, if so, on what authorities (legal) or reasoning (non-legal) are these sweeping assertions based ?

Does the hypothetical involve a criminal case where evidence is offered which was derived from the interrogation ?