Dividing property - options and impacts on fire department access

Regarding point 3: We want to avoid demolishing the adjacent outbuilding (rather the barn, if anything). It is structurally sound, has a relatively new roof, and contains rooms that we would like to continue using (garage, cellar, workshop, summer kitchen, even an old stone oven that still works). The building serves some functions that allow us to dimension the new construction about 20-25 sqm smaller. What speaks against permanently routing the pedestrian and vehicle right corridor over the courtyard?

That means: You are mainly interested in the building plot for yourself, and that the financing of your building plot cannot jeopardize grandma’s right of residence; dividing the property for easier later sale of a part of the property (don’t forget inheritance tax as a motive for sale!) is basically not an issue, the entire property is to serve family living forever? – then (but only then!) it is not a disadvantage for anyone if the right-of-way corridor permanently "cuts through" property "A," since it does not impose any use restrictions beyond a parking ban.

You are actually only interested in the building plot for yourself, and that the financing of your building plot cannot jeopardize grandma's right of residence; a subdivision of the property to facilitate the later sale of part of the property (inheritance tax as a sales motive not to be forgotten!) is actually not an issue, the entire property is to serve only family living for all eternity?

That is exactly right. What type of transfer of ownership does this constellation then suggest?

For which type of transfer of ownership does this constellation then speak?

Primarily for no transfer of ownership at all, I then see a condominium ownership to be weighed against a heritable building right (and I can gladly connect you with a lawyer from my network specializing in inheritance law, a notary only comes into play later).

Exactly.

What type of transfer of ownership does this constellation speak for?

In my opinion, this makes no difference for the type of division, except that a "Pfeifenkopf" division is excluded.
But the "worst case" seemed important to you, and then strangers would use the path across your own yard. How likely that is (insolvency) you have to consider. If the right of way goes across the yard, I would also lay the line there.

Some pros and cons:

Ideal division:
No surveying costs, higher notary costs, division declaration "difficult" to consider the worst case, very precise definition of responsibilities, cost sharing, common areas, SNRs necessary (I am not a fan of that, does not seem to see it as critically). Financing? (<-- talk to the bank).
Real division with right of way:
Surveying costs, notary costs based on the value of the rear property, no real estate transfer tax if in a direct line (grandma). Financing simple, probably cheaper, more banks to choose from.
Transfer with usufruct:
Probably lowest costs (value of entire property minus usufruct value). If grandma is in first rank, also no danger in the "worst case," but financing in second rank possibly difficult (<-- talk to the bank).

I would tend towards 2 or 3, also because WEGs are their own legal area, which can hold many pitfalls and costs if necessary. Whether 2 or 3 depends mainly on the financial situation, i.e. how much of the house needs to be financed. (<-- talk to the bank).

P.S.: Heritable building rights are then the 4th option ;-) But why not.