I think it's hard to tell whether the verb, sunt, is telling is WHERE the girls are (Puellae sunt in ludo), or whether it's telling us that they are QUIET (Puellae sunt tacitae).
The separation of Puellae and tacitae may suggest that the adj. is being asserted (i.e., that the girls are quiet).
Tacitae sunt puellae quae in ludo sedent/discunt/student: The girls who sit/learn/study in school are quiet.
A single noun phrase is "the quiet girls" ~ "puellae tacitae".
Interrupt it with a verb and now you have a whole sentence: a subject, the verb, and a subject complement.
"Puellae sunt tacitae" ~ "The girls are quiet."
"They are quiet girls" ~ "[Eae] sunt puellae tacitae."
No. Transitivity does not even apply to stative verbs. Transitivity only applies to active verbs.
Active verbs are verbs of action. Something is happening. If they are transitive, there is a direct object to receive the action. If they are intransitive, there is nothing being acted upon.
I walk -- intransitive
I mow the lawn -- transitive
Stative verbs are verbs of state. Nothing is happening, they are just describing or defining the subject.
I am a woman.
He looks tired.
This seems easy.
The pie smells delicious.
The blanket feels soft.