A handy man and his assistant could do it, if they can read the instructions for the stacking kit. You may also need a longer cord for the dryer, depending on where the plug is located. And some right-angle thingies for the dryer vent.

1) You can brace or block the joists per standard construction, but what might be easier is to strap the bottom edges of the joists. Typical strapping is done with a 1x3, but a lot of times I'll simply use a 2x4. Run a 2x4 across the bottoms of the joists, perpendicular to the joists. Add a dab of PL adhesive and use a couple of screws at each fastening point. You have specific needs here, so spacing the 2x4s as you need will work very well. What it does is if a single joist wants to deflect downward, the strapping transfers that load to the adjacent joists as well. So it's good as a floor stiffener. For a washer/dryer set up, it also dampens the entire floor platform in terms of the possibility of the spin cycle causing the floor to reverberate. The strapping serves the same purpose as cross-bracing or solid blocking between the joists. It's code-approved, though code only requires it for 2x12 joists, with the strapping being made of 1x3, and the strapping spaced every 8'. The strapping is more effective long-term than bracing or blocking, due to fitment, installation, and shrinkage issues. 2) Do the whole floor. There are only restrictions on maximum spacing (every 8'). So if you make it every 2', or 3', or 4', no worries. Strapping is also easier because you're not wrestling with any of the utilities that take up space between the joists. 3) Your joists span 8-1/2'. For simplicity, why not do run three pieces of strapping? One at 1/4 span, one at half-span, the other at 3/4 span. Just a little over 2' spacing. 4) 3/4" ply over the diagonal boards is plenty. It does not have to be exterior grade. 5) Your floor sandwich can be made up of: -Tile -Ditra -Floor heat wires encased in SLC (no wires under the washer/dryer area through, see comments later) -Plywood underlayment covered with SLC primer -Diagonal plank subfloor -joists I usually advocate a small platform under the washer/dryer stack. It's more for damping than load spreading. I've done sandwiches of plywood/cement_board/plywood, or plywood/MLV/plywood. MLV is mass-loaded vinyl. Screw through the top layer of ply, through the middle material, and into the bottom layer of plywood to secure it together. Or just use construction adhesive. I drill a hole through the middle of the platform sandwich to accommodate the flood pan's drain line. I usually put a square of rug pad on the floor. The inexpensive, maybe 1/8" thick, rubbery mesh or open weave type of rug pad. It acts as a bit of a damper, but also holds the platform in place. I then set the platform on the rug pad. Then put the flood pan over the platform with the drain plumbed through the hole in the platform. Then set the washer in place and the dryer on top of that. I recommend you tile the entire floor, but again, no heating wires under the location of the washer. You'll be putting the sandwich platform on top of the tile in that area, and the insulative value of that platform can shorten the life span of the heating element. Pricklypear, the Ditra-XL is simply thicker than regular Ditra. It really wasn't designed for a specific tile size. It's sole purpose is to allow the thickness of "Ditra plus tile" to match up with the thickness of a typical hardwood floor.

Thanks - There appears to be options to side vent. I'm worried that 7" on the side is not enough as the dryer my parents have sticks out 9" when you take into account how much the pipe protrudes from the side, and the width of the elbow. Going out the back worries me because according to the calculations, I only have 4.25" of space. The install guide says i need at least 5". I guess a periscope would work, but i read that its a less than ideal solution as it can restrict air flow I really dont want to buy these machines and then realize they dont fit. I guess in the worse situation, i can cut out some of the drywall to make room for the pipes. It would get hidden anyways

What do you need in your laundry space. I like many of the ideas that others have posted. I would suspect you need hanging space. Ironing space. Storage space. dirty laundry hampers. storage for brooms, and vacuum possibly. If you go with a built in, I would do generic sizing for machines, so that you can switch out brands. The best idea I think is to have side by side single set in basement and another set near the bedrooms. The side by side allows the water shut off and drain to be above the counter for easy access. You might have to move out the dryer for vent maintenance, unless you go with a ventless model. You absolutely need access quickly to water valves and dryer vent, and electrical outlets. I don't see that in your plan. I have a small built in cabinetry and w/d on my main floor. It is perfect for our family of 2. When I planned for the main floor built in, I did all the design myself. I have an access to one side to get to the water shut off valve, drain pipe, and dryer vent (for clean out). I can reach into the lower cabinet open area to access the electrical outlets. I have about an inch on either side of the built in, and it is not a problem sliding the set out. I do not have a pan under the set, after a lot of thought. My machine pump clean-out is in the front of the washer, so no need to move the machines. When I was moving the machines in and out during the remodel, it was no big deal to slide the machines out. But that is a rare instance. There are several inches at the top of the machines. This set up is custom to my Miele set which is of a smaller design. The room was a constraint for size. I am not sure if a Bosch set will fit, but that could be an alternative set for me in the future, if needed. I always shut my water off when we leave for a few days. I also have a double stacked set in the basement of used machines for my DH farm clothes. I always shut the water off after my weekly farm clothes wash up.