I suggest deleting secular marriages - replace with secular civil unions open to consenting adults, with the same extremely-hard-to-break-by-nonparticipant legal advantages as current marriages, and move as many of the financial benefits as prudent to the civil unions that are raising children. Certain financial benefits would still accrue to childless unions (inheritance, mainly), but I'm OK with that - death taxes strike me as bizarre; the government had their shot at the money while the person was alive.
Marriage is left in the hands of the church, and civil unions are created as a sheaf of contract rights that are standardised (so the entrants don't need a lawyer) and protected against third-party meddling to a greater extent than a typical contract.