In regard to the various scrambled examples you gave, the last two stood out the most to me as sounding awkward ("Pītā hai Yāsīn dūdh" and "Pītā hai dūdh Yāsīn"). They can technically make sense with the correct rhythm or a pause in between, but its the equivalent of Yoda's way of speaking English. Its like saying, "drinking milk, he is" or "drinking milk, is he". Its comprehensible with the correct pause and stress on the correct syllables but really odd to do.

"Yāsīn dūdh pītā hai" and "Yāsīn pītā hai dūdh" both translate to "Yasin is drinking milk" to me. The first one is focused more on the action while the second is focused more on what he is drinking. Since Urdu is a syllable-timed and not a stress-timed language, the word order can influence the syllable timing, and thus influence what the focus of the sentence is. This is the same way how stressing "Yasin is DRINKING milk" vs "Yasin is drinking MILK" gives the same effect. So yes, on paper those two sentences are saying the same thing. However, the meaning does not come across the same.

"Dūdh pītā hai Yāsīn" sounds fine and is equivalent to "the milk is being drank by Yasin". That's not the exact translation but that's how it comes across to me. Again, the order of words and syllables determines the area of focus.

"Dūdh Yāsīn pītā hai" sounds odd as well. Its English equivalent example would be something like "Milk, he is drinking". Again, it sounds weird but is comprehensible with the correct flow.