Engage the services of a local talented architect that can properly evaluate our project and help design a home with you that meets your needs and takes into account the existing conditions of your site.

Agreed, this is ideally the best option, however those we have talked to have already expanded the scope of our project and now want to demolish the garage to build a guest house in the same spot which leads me wonder if the person getting paid for the job is truly a neutral opinion?

You arent saving enough thst isn’t getting touched to make it worth it. It’s far easier to knock everything down and start over.

Trying to morph the existing garage into something it isn't could very well cost more than starting over, particularly if you're going to alter the roof pitch.

The only reason to keep an older existing structure is if its location is grandfathered in under older setbacks requirements. If setbacks haven't changed and you won't need any variances, then I would probably knock down and start fresh.

It’s location is grandfathered in since it just barely sits across two lot lines... and new setbacks require 5ft from lot lines with a new build. Another decision we find ourselves facing is whether to re-plat to 1 lot and build across both or put the new house build on the larger single lot and leave the smaller lot for a future guest house or other use. (So many decisions 🤪)

You will need an architect regardless of the direction you choose. Be firm up front, and state exactly how you see the scope of the project. It seems unlikely that anyone on an internet site can adequately assess your options. Good luck with your new home.