If you can come up with the money to get some of these convertible units, the space can be even more versatile. I got the Expand coffee table that converts from a short table that fits easily in front of the sofa, to a full dining height table twice the size. I can use my sofa as "booth" seating and pull up four chairs and seat six! Something as simple as the lift and storage bed can give your sister so much more usability of her space. So can a console that pulls out to be a dining table, or a table that folds into the wall. I bet if you did a search on YouTube you could find some place to buy the plans for making some of these things. Expand Furniture in Vancouver, BC, CA I know that the tiny homes shows on TV use the bed lift storage systems, so they must be for sale. Wayfair sells a ton of storage coffee tables that convert to bring a writing or dining surface up to the person seated on a chair or couch. It is not all expensive, either! There is often a space under the surface that can store things, too. Don't forget to use the wall cavities between studs for storage whenever you can. I have seen nice toilet brush and plunger cabinets next to toilets, recessed niches for display (with a light at top), and spice storage for kitchens. WG Wood Products will give your husband lots of ideas for using wall storage.

Your first step is a paid assessment from a good general contractor. They will look at where your sewer leaves the house, where your electrical box is located, and how much electrical service it has. And assess foundation and framing, and how to properly insulate. He will discuss how to get those needed utility services to your garage, and any upgrades that may be required to make that happen. That will drive the placement of your kitchen and bath in any layout. It has to be done first to even know if the project is possible. Just like the design documents required to be filed by your city, if your husband is unable to do this, he is not qualified to be doing the job at all, and you need to factor in contractor labor for the majority of the project, as well as design costs. While there are some very capable DIYers, there are also some that choose to do so without the needed skills. Do not get in over your head with DIY anything here. This is how people lose their CO's when they can't get the work done correctly or timely. You only have so much open time on a permit. And all of your work must pass inspection.

I have schemed different scenarios - moving the kitchen to either wall, eliminating Dining, moving Laundry, reducing one bedroom to 9' - and none of them seem to support an island. You can do the math: 24" cabinet + 36" [yikes!] aisle + 24" [seating only] island = 7'-4 1/2". Your Living is 18'-6" one way and 17-9" the other, so subtract the 7'-4 1/2" and you are only left with about 11'. For a Living Room, you need a good 10' plus circulation (you do not want a couch backing to window). Especially since you have 2 bedrooms. I would even postulate you need a Dining table for 3-4 residents. I see why the architect has the placement of windows as they are, albeit without elevations showing the ADU sitting under your deck. For the tv, simply make the side window a transom for a tv below it. I would suggest going back to your competent architect and prioritize your criteria - a small ADU cannot be all for everything - and be willing to lose something - like a bedroom, if you really want that island and a cooking, viewing, and eating space is the priority.

Definite "NO" to switching the stove and sink! That puts the stove in the middle of the work flow, and the sink needs to be the pivot point in the work area. One has to work back and forth from the sink to the other appliances/work areas. I also agree with the comment about the need for a window and working with landscaping/fencing, etc. It's frustrating that so many people who design kitchens are not the ones who have to work in them day in and day out! The refrigerator also needs to be on the wall next to the entry doors/patio doors (whatever those doors are...) to facilitate people coming in and grabbing food or drinks without having to walk through the kitchen or living area ...interrupting work and tracking dirt through. Such an arrangement can also actually enable 2 individuals to work comfortably in such a small space...(voice of experience here!) Also...regarding the comment regarding eliminating a bathroom in favor of more storage...while increased storage would be a definite plus, (I'm always in favor of more storage...) the "luxury" of having 2 full baths in this small home could also enable 2 single adults to share it...or parents with an older child...or with a couple of smaller children. So it increases the possible renter base for you.