Meaning of phrases

Dear Teacher,

I meet these sentences:

There were six or seven buildings of poured concrete, each three stories high, with screened-in porches punctuating the low clean lines.

Question: what's the meaning of screened-in? the low clean lines?

The license disappeared (into a crack) smoothly, like a bank card being sucked into an instant-cash machine.

Question: what's the meaning of an instant-cash machine? Please explain this kind of machine. Is it a ATM?

Just off the balcony, I could see palm trees with little beaded skirts near the top.

Question: what's the meaning of "little beaded skirts near the top"?

there were only lush green treetops visible

Question: please explain the grammatical function visible? Which word does it modify?

Pat Usher was having a better time than I was too, and I resented that. I went at it (conversation) again. Was it Mrs. Peacock in the library with the rope?

Question: please explain the meaning of the last sentence: Was it Mrs. Peacock in the library with the rope?

Thanks.