"They knew well what they were doing!"
Translation:Ei au știut bine ce fac!
Probably yes - though it sounds weird in English, but in some other languages with not that many tenses it is normal.
In this case "they" performed the action, and "I" am a spectator. From my spectator point of view, both "they knew" and "they were doing" were happening in the past, so English uses Past tense. But from "their" point of view, at the very same moment they knew, they "were doing" in the present. Following this logic, spectator says that "Ei au știut" in the past, but they "fac" in present, because when they knew it, it was present time for them. I believe this part of Romanian is logically similar to what we have in Ukrainian (Вони знали, що роблять).
Another case could be "They knew well what they had done" - probably this would be translated like: "Ei au știut bine ce au facut"
(native speakers, please confirm or reject)
I think that "au stiut ce fac" is the translation for "they knew what to do", meaning they were not doing it yet, but they already had a plan; while "they knew what they were doing" means they were already doing it with full awareness. I wonder if "au stiut ce faceau" wouldn't be a better translation.
To clarify, for those unsure, if somebody does something (usually something not good) and then claims it was done unintentionally, yet you don't believe them, we're likely to say "they knew full well what they were doing!", i.e. "I don't believe it was unintentional at all, I think they did it deliberately." The sentence example here does work without the "full" but probably feels a little sloppy in English.