What is the jurisprudential school to which a married couple, differing in madhhab, should refer when they disagree on a certain issue?

The spouses should refer to what is preponderant based on evidence. Each of them may follow their own madhhab (school of thought) or someone whose religiosity and piety they trust. Neither is obligated to follow the other unless the correctness of the other's madhhab and the strength of their evidence become clear to them. If they are unable to distinguish between the evidences, then they should follow someone who adheres to their own madhhab, based on the Almighty's saying: "So ask the people of the message if you do not know" (An-Nahl: 43). If they are capable of critical reasoning, then they must refer to what is preponderant; otherwise, each of them may follow their own madhhab. The wife is not obliged to follow the husband in his madhhab.