I just hired a new architect and am making arrangements to have my construction crew in CA to finish up both of the projects. 

Would an architect or engineer that works in the residential industry, such as designing ADUs, additions, custom homes, etc. qualify as a real estate professional in the eyes of the IRS?

I Landlord (Lady lol) in Danbury and yes it can go very well or very wrong.As an architect, I salivate over all those beautiful old houses in Bport.  

The bathrooms would be directly above each other) We have drawn up a basic floorplan ourselves but we would still have to hire an architect etc.

If you are trying to get into new construction without prior experience I would align yourself with a trustworthy GC, Civil Engineer, Architect, and Permitting Atty; ideally with experience in the areas you are considering.

I think the first step of the process is getting the land surveyed and speaking with an architect.  

Work with an Architect who will also pull permits along with drawings.

Network and build connections with architects, contractors, land surveyors and even other investors who may have a background. 

Reach out to a contractor for some numbers or better yet to an architect to have some preliminary plans drawn.Also keep in mind that material prices are currently very volatile and contractors most likely will not be locking in prices.

lmaoIF your Dad is "going to build a duplex" AND you still want to be involved in the RE industry... ask him to show you what he can or wants to... all he can: from the planning, budgeting/financing, scope of work, drafting of plans or hiring of a Designer/Architect, dealing with the city and Codes, the GC, subs (or if he lets the GC do it all), etc etc ...