Frank,
sounds like you want a flagstone patio? Not sure which is best. It seems like the grout would inhibit grass/weed growth better than sand.
But even with sand, you should have a fairly thick base down.

I was thinking of doing a flagstone path in a high traffic area in my lawn. I seen someone just countersink them and let the grass grow naturally around them. Nice look IMO.
-jasper

I'm guessing you're in a warm zone and so you don't need a crush gravel base to prevent frost heave as you might in colder areas. You can lay just over sand, or even just over lawn or dirt, if you remove the grass first - this is never the recommended method, but sometimes we do what we can, not what we should.

If you're not removing the lawn you'll have to use mortar between the cracks, as grass will probably grow up happily through sand. But I wouldn't bet the estate on it not growing through mortar either, unless you get it real thick and solid, and even then you may be foiled by cracks if you don't get it totally well supported.