Tearing up the yard for sprinklers--going green from here on out...how?

Alright, we've torn up the concrete around our 50 year old property.  Next we're tearing up the lawn to put down PVC sprinklers (there are a few sparsely-placed metal ones that are rusted to holes).  My FIL wants to dump poison on the whole yard (including onto the crabgrass surrounding my organic garden box  ) and go from there.
I want an organically-grown lawn for my kids to play on.
What do I do?  Start w/ tearing up the lawn...then talk to me like I'm 5 (much more likely to make sense  )

Oh--I live in Northern California.  Warm to hot most of the year, and rainy only in Winter.  I'd like a lawn my kids and I want to roll around on--not one that pierces my feet like it does now   The more drought resistent the better.  Costs a boatload to water here and we occasionally have water restrictions, tho not often.

I'm not sure what "50 year old property" means.  Wouldn't it be thousands if not millions of years old?

Have you read the article at richsoil.com/lawn

Yes, I definitely read it.  I'm just not sure how to proceed w/ completely reseeding/killing the weeds in the lawn organically.  We need to seed this summer, so one recommendatio I read about Soil Solarization would take a few too many weeks to kill the weeds.

By 50-year old lawn, I mean it was seeded 50 years ago when first built and nothing's been done to it since.  We did aerate it, but didn't do a whole lot of good...

It sounds like you are willing to spend money and time for instant results.  Yes?

I think my web page is about using less time (mow less often, water less often) and little money to end up with a great lawn in a few months to a few years. 

But if you are after quick results:  Import top soil - that will smother the existing grass.  Plant tall fescue on top of that.

But maybe you don't need to bring in more topsoil.  Maybe your existing soil is fine? 

Grass that has been growing for 50 years can still be good grass.  Yes there are better seeds now.  But they cost.

What does your existing soil look like?  How deep is it?  What is your subsoil made of?