Genitive plural personal nouns in 1st and 2nd declension: I am wondering how human possessors of mixed gender were treated in ancient Latin. For example, how would the following possessive be translated: 'This is the home of Mr and Mrs Catullus (i.e. of the Catulluses)? I suspect that the Romans would have used the masculine ending.
As a general rule, groups containing both men and women take the masculine in Latin. For example, a male friend is an amīcus (masculine), and a female friend is an amīca (feminine). But a group of friends of mixed genders will always be amīcī, masculine plural.
However, family names were a bit different in Roman times: they didn't quite have equivalents for "Mr" and "Mrs", and instead of saying "the Juliuses" (Juliī) they would generally use "the Julian clan" (gens Julia). If you wanted to be really pretentious, you'd use a Greek form: the Cornelius Scipio bloodline (as in Africanus) preferred to be called the Scīpiadae. And since clan was determined by birth rather than marriage, the wife of Cornelius wouldn't be in the gens Cornelia herself (unless she'd been born into it).
So in your particular case, if you're using ancient Roman names, it might be best to just use two separate genitives: ecce domus Corneliī Flaviaeque "behold, the house of Cornelius and Flavia".
In such cases the masculine noun takes precedence (Pinkster 2015, Chapter 13: Agreement).
I found a good example in Pinkster 2015 (example (c) on p. 1285):
... propter summam et doctoris auctoritatem et urbis quorum alter te scientia augere potest altera exemplis (Cic. Off. 1.1.1)
doctoris - GEN.SG.M., urbis - GEN.SG.F., quorum - GEN.PL.M.