"Kati is painting workers and engineers."
Translation:Kati munkásokat és mérnököket fest.
So, if a noun ends in -ás it will always get -ásokat in plural accusative?
Most likely yes, but there is no such rule. We could carefully say that the second connecting wowel, although of the same set of the "wowel harmony", differs from the first one.
Cf. "mérnök" accusative "mérnököt" plural "mérnökök" --> you would say yup! after "ö" the coinnecting wowel is also "ö", consequently the plural accusative must be "*mérnökököt": but no, it is "mérnököket".
No I would not say ö, since there is no such ending available, if I've understood correctly. Isn't the rule that only -at/-et are allowed in plural accusative? So my question is actually, could -às ever result in -ásoket in plural accusative?
You are absolutely right, if the connecting vowel between the word ending and the accusative suffix can only be "a" or "e", then it is impossible that a high order "e" connecting vowel follows a low order connecting vowel "o" (-ásoket) because it would violate the "vowel harmony".