The sentence below is pretty straightforward in terms of word order (it is what I frequently encountered in passive voice):
todos los coches están vendidas
But I think that the one below is also grammatically correct and the word order (in ser + past participle) depends on what you want to accentuate - either that "ALL the cars are sold" or "All the cars are SOLD". Please correct me if I am WRONG.
están vendidas todos los coches
As for pasiva refleja (se + singular/plural verb in 3rd person) for me it doesn't seem so clear. For example, what is the difference between two sentences below and are BOTH of the correct or only ONE of them?
Se venden coches aquí.
vs
Coches se venden aquí.
Seems that not only me who is confused, because I noticed that explanations differed for el ratón se mató vs Se mató al ratón in the following thread: Preterit Passive vs. Estar + Past Participle.
BUT by looking at another question Dos formas por una función: "ser+participio" y "se pasiva" para referirse a algo en voz pasiva, I found the following:
"La pasiva con "se" permite mayor flexibilidad en el orden sintáctico y esto ofrece una mayor versatilidad estilística: "Cada año se celebra la fiesta en un lugar diferente" (NO "Cada año es celebrada la fiesta en un lugar diferente")."
So I guess you cannot say "están vendidas todos los coches". But still am having doubts regarding word order when using "Se".