You might ask over in the Kitchens forum as well as here, since that's more of a lifestyle issue.

If you're designing a new kitchen for your dream house (which I'm getting from your name), you can design it so that the unloading of the dishwasher(s) is easy. Plus, if your kids are in school, they can be responsible for that too.

So. How are you at putting away hand washed dishes? Better than machine washed dishes? If so, why?

Modern dishwashers usually take two hours to run, plus dishes chip less if you put them away cool, so that's more time. With a family of at least six, that's a lot of time waiting for clean dishes. Add to that, new dishwashers are supposed to use a lot less water than hand washing, so people are encouraged to put everything possible in them (not considered decadent anymore!), and you have another reason to be advised to have two. I think these are the reasons so many people are putting in two nowadays.

Some people love the drawers, some hate them. They do have a learning curve to figure out how to most efficiently fill them. If you can get your average whole table full of dishes into either one of the drawers, I can see a scenario where you put the table dishes in one drawer, and the cooking, prep, snack, and extra glasses in a regular, full sized unit, with one drawer being run after each meal, and the other emptied and returned to the table, and the standard unit being run whenever it's full, more likely, once a day, or maybe once after lunch, and once after dinner. That's probably idealized, however, and hard to make work in real life.

What I have learned from people who have two dishwashers is that they're best in the same place, or at most a pivot apart, because inevitably there's room in one unit and not the other and everything gets all mixed up together.

I don't know anyone who has two double drawer style units (i.e., four drawers). Most who have two, have two regular ones. A few have one of each.

We bought a house 20 years ago that came with 2 dishwashers; at the time, I thought that was over the top but learned otherwise. We installed 2 dishwashers in the house we built 4 years ago. I considered having 1 be drawers & the other conventional, & decided on 2 conventional for the following reasons: both operate & load the same, dishes load completely into one & then the other rather than spreading them out, & we had some concerns over drawer reliability & utilization. We chose the same model Miele for both, & installed them flanking the cleanup sink. This makes for more efficient loading/unloading (rather than putting them in two different locations). Our dishes & tableware store across the aisle from the dishwashers so that kids can safely set the table & unload the DWs. Our Miele model has very flexible rack options, and we can even remove the middle rack for tall or large items, which I use for items like cutting boards. (If we had drawers I'd only be able to do this with the conventional DW.) One is hooked to cold water & the other to hot; if I did it again I'd hook them both up to cold. Only the cold can run the China cycle & I don't see a measurable time difference with the hot. We generally alternate the dishwashers (unless we know we want the China cycle), and because they're integrated, we "mark" the one running with a clip on the handle because they run so silently & the run light isn't obvious, and it also means don't put dirty dishes in with the clean (unload it!).

With the size of your family, you won't be as concerned about partial loads, which the drawers help with. Our Miele has a Sensor cycle which can adjust the run time for partial loads.

Our one DW gets filled up so fast, and it is one of the more spacious brands (the Kitchenaid). One teenager still at home -let me tell you, one teenager uses up the same amount of dishes as 4 grade-schoolers, I am not sure why, but teenagers are just like that. If you have 4 grade-schoolers now, imagine the dish usage as they get bigger and eat more, and eat more frequently, and eventually, become teenagers. If we had the space, we'd have two DW's. My advice is to go for two, and I wouldn't fool around with the dish drawers. The drawers are nice, but can be fussy to use, and I think you're going to need two full-capacity DW's.

I did not put in two DWs in my kitchen remodel but this is one thing that I regret. I really wish that I had put in 2 DWs. (I don't have the room, but I can dream!) Many families I know have done this and they love it.
I find that my most time consuming chore in the kitchen is the clean up and not the cooking. At the end of the day, when the DW is full, I am forced to wash the pots and pans by hand. We cook nearly every meal and we end up with alot of pots and pans. If I had 2 DWs, I would be able to put most of my pots and pans in the DWs during our dinner clean up. It is too impractical to wait for the DW to be done which takes 2 hours. I am too neurotic to leave the dirty pots and pans in the sink until the next morning to be loaded into the DW. I really like going to bed with the clean kitchen.

If you can actually organize your day so that dinner starts with an empty DW (which would mean making sure the dishes are ran before dinner) then you may be able to put the pots and pans in the same load of dishes after dinner and make 1 DW function efficiently for you.

Regarding cold versus hot water hook up: I have a Miele also. My hot water is so far from the DW that there is NO REAL HOT water entering the DW. It is only luke warm. You can test this by checking the water at the bottom of the DW after it has filled. Depending on where your hot water source is, it maybe a moot point regarding hot versus cold water hook up. I run the china cycle without worrying about the temperature since I know that there is only lukewarm water in the DW from the water source.