Mmm... I (native AmE) wouldn't necessarily say so.
Jak (how) is an adverb, but what we have in the Czech sentence (jaká) is an adjective. Drawing on VladaFu's earlier comment, I'd put it closer to "What kind of names are your daughters'?" (Note the plural possessive.)
But if "How are the daughters named?" is something that works for you, by all means, use it, and it may help others, too. I'm a big fan of in-my-head translation workarounds! :-)
If somebody ask me this Czech sentence, I will think of answers like "short", "nice", "hebrew" - some attributes of the names (maybe translatable as "How are the names of your daughters?" rather than "What are the names...". Asking for the names, the sentence should be "Jak se jmenují tvé dcery?"