Barrier-free single-family house floor plan for aging with parents' bedroom on the ground floor

We would like to build accessible right now

The ground floor is not accessible. Please complete the questionnaire in full.

for me it is initially purely about the floor plan on the ground floor, I have been stuck on it for weeks.

Then get off it again and start with the upper floor. Otherwise, when deriving the upper floor from the ground floor later, you can still get much more confused. From top to bottom is easier (at least in the normal case with entrance on the ground floor, on a slope it can be different).

What does barrier-free mean for you in old age?
You have no stairs and thresholds.

For rollators, nursing services, etc., it is completely unsuitable. The planner has probably never planned in this direction.

... By the way, how wide are the doors, meaning the actual door leaf measurement?

For a wheelchair, etc., they should have at least 90 cm clearance, right?

For a wheelchair, etc., shouldn't there be at least a 90 cm passage?

For a wheelchair you need a turning circle of 1.50 m. Everywhere you move.
There is a distinction between low-barrier, barrier-free, and age-appropriate layout.
In "barrier-free or low-barrier house construction," you should avoid long distances and unnecessary corners where it is difficult or impossible to get around. Bedroom/dressing room/bathroom is such a case.
Enclosed rooms would not be suitable because of caregiving staff.
If you want to build age-appropriately, then make sure that a stairlift has space in the hallway so that you don’t have a ghost floor in old age and can also occasionally take care of grandchildren who then sleep upstairs.
Basically, one can say that only a ground floor without an upper floor is debatable, since the stairs are the most important element; after that come the load-bearing walls, and window positioning is also not unimportant. Everything is interdependent.

The consultant drew us a floor plan, but I find the solution with the master bathroom unfortunate. Also, because of the huge ground floor, the upper floor becomes accordingly large, where we don’t need that much space.

That is due to your wish.
Is two-story construction a must according to the development plan?
Otherwise, I would recommend a single-story house with an attic conversion, where the knee wall is properly high or an area is not developed.

If you do not construct the walls in the bedroom / dressing room / bathroom area on the ground floor as load-bearing, you can create accessibility if needed.