- They live the quiet life on farms
- They live the quiet life in farms
Which is correct?
Which is correct?
It depends on what they are. If they're people I would say, "they live on farms", but I can imagine using "in farms" when talking about insects.
This isn't really a matter of "grammatically correct". They're both valid, but on is more common...

While I suppose that one could say they lived in a farm, it strikes me as being incorrect. It's extremely uncommon in American English; I've never seen nor heard that before today.
If you say that they live in a farm, it suggests that they live inside of the farm. Using in as the preposition, it would be much more common to say they lived in a farmhouse or they lived in a house on a farm.
In is generally used to mean inside, within, or into.
And now a voice from west of the pond.
We never say in a farm. One lives on a farm. I can't think of a usage for in relative to farm; even when we want to say that some object or building exists within the confines of Farmer Brown's farm, we say (for example) "that tractor is on Farmer Brown's farm." Not in.
We never say on the weekend. We say this weekend, next weekend, last weekend, or various other structures that do not involve prepositions, as in I'm going to the beach the weekend after next.
As it happens, many of us do say wait on line, just as you say Londoners do; it's becoming more common over here, although wait in line still seems to be the standard usage over here.
And just for good measure, we would never imagine anyone lives a quiet life on an American farm. These days farms, generally speaking, are work intensive places which, for the most part, are on the brink of financial disaster, and are bustling with activity and filled with the sounds of numerous large animals, heavy equipment, and many people hard at work from long before the sun is up until long after the sun goes down.