Missing marriage cert

More than likely they will accept the census records and newspaper announcements to be sufficient. I couldn't find the marriage certificate for my own grandparents, and luckily my grandfather was still around to write me an affidavit which sufficed. The birth certificate of their child will also show the mother and father's names, so I would expect that you won't run into issues. Just give them a call on the infoline or send an email to get confirmation. My lineage was strictly the paternal line so none of the citizenship via marriage questions arose, but that's the only place I would fathom any issues.

Good luck!