"You have three clever daughters."
Translation:Tres filias callidas habetis.
it is "you" who has the daughters we are discussing.
And that is exactly why "you" is in the nominative case -- because it's the subject of the verb. (Who or what has? -- subject)
The daughters are in the accusative case because they are the direct object of the verb: the thing which "is had".
- Filiae callidae psittacos iratos habent. "The clever girls have angry parrots." (girls - subject; they "do the having")
- Pater et mater filias callidas habent. "The fater and the mother have clever girls." (girls - object; they "are being had")
And in the singular:
- Filia callida ad ludum it. "The clever girl goes to the school." (girl - subject)
- Filiam callidam video. "I see the clever girl."
OK, so if the daughters are in the accusative since it is they who are the direct object of the verb, then where does the genitive fit in? Would that be something which is in a sense owned by the object, for instance:
"The dog is walking on the road" (canis in viam ambulat). In this sense the road is "owned" by the dog since it is the subject of the dog's action?
where does the genitive fit in?
To a first approximation, it works like "of" in English, e.g. nomen filiae callidae "the name of the clever daughter", nomina filiarum callidarum "the names of the clever daughters".
"The dog is walking on the road" (canis in viam ambulat).
You seem to be mixing up two sentences.
- Canis in via ambulat. = The dog is walking on the road.
- Canis in viam ambulat. = The dog is walking onto the road.
in + ablative for location; in + accusative for destination of motion.
In this sense the road is "owned" by the dog since it is the subject of the dog's action?
No. The preposition in assigns the case here (ablative or accusative); the subject is completely irrelevant. There is no ownership involved here.
Yes, tria is a neuter plural nominative/accusative (in form very much like omnia , which means "all things," or "everything").
In the 3rd declension, masc. and femin. nouns & adjectives are not differentiated from each other: so, trēs is a masculine/feminine, nominative/accusative plural form.
There are: tria vehicula "three vehicles" (neuter); trēs fīliae (nomin) and trēs fīliās (accus) "three daughters": trēs fīliī (nomin) and trēs fīliōs (accus) "three sons."
In the other cases, all genders are the same, for the word "three": genitive plural trium goes with vehiculōrum and fīliārum and fīliōrum ; dative/ablative plural tribus goes with vehiculīs and fīliīs and fīliābus .