I'd like a little context for those sentences-- they don't immediately have exactly one meaning to me and might be ambiguous. But I'd need to imagine some contexts to know whether that really works out. They're low frequency, certainly!

My intuitions:

Lily whined to Marlene for Nedra to keep quiet

Lily complained to Marlene in order to make Nedra quiet.
Either Marlene would ask Nedra to be quiet (1), or Nedra would decide to be quiet because Lily was complaining (2).
"Lily complained to Marlene to get the volume turned down on the TV" (1)
"The student complained to the teacher in order to get her peer to stop cheating." (an indirect threat, 2)

Lily whined for Nedra to keep quiet

Lily expressed her desire, via whining, for Nedra to be quiet.
Possibly this is a complaint directed at Nedra, but I don't think it must be.

Lily whined to Marlene to keep quiet

"Marlene, be quiet", Lily whined.
Or
"Lily whined to Marlene so that she [Lily] was distracted enough from speaking to the other group" ("The angry politician complained to his friend in order to avoid yelling in front of the voters.")

Lily whined to keep quiet

Awkward. Maybe "Keep quiet", Lily whined. But awkward/choppy. Something seems to be missing, maybe in the right context-- 'They arrived at the haunted house, and Lily was scared. Turning to her friend, Lily whined to keep quiet... "I'm scared!"'
But this is more likely just:
Lily whined in order to stay quiet-- whining instead of speaking loudly. (Odd meaning, acceptable syntax.)


As for your readings:

1. Lily ordered Marlene to keep Nedra quiet

Possibly. Awkward. Probably what the original sentence was intended to convey.

2. Lily ordered someone to keep Nedra quiet

Maybe. But including Nedra herself. "I hope Nedra is quiet!!!", etc.

3. Lily ordered Marlene to keep people quiet

Unlikely. Marlene should be quiet here. "to keep quiet" isn't a general order for people in general. It's usually specific.

4. Lily ordered people to keep themselves quiet

Maybe. As I said above, this is awkward.



I hope that's somewhat helpful. These are weird sentences.

Generally speaking, "for" introduces a subject for the infinite:
"I asked for you to complete the assignment."

Generally "for" is not pronounced when the subject is the same as the matrix subject:
I try to sleep.
But in older English (Middle English) and in some dialects, you find "for to":
I try for to sleep.

It also may be some sort of oblique argument for the matrix verb, but that's not entirely clear.

Also, in the last example "Lily whined to keep quiet", the question is "to whom?".

No idea. Without context, that's basically meaningless to me.
(The alternative reading is fine, if odd, "whined in order to remain quiet".)

Even in a situation where this would make sense contextually, it's still bizarre:
??The prison guards screamed to stay quiet.
I'm tempted to mark that as ungrammatical.