An update from me at this point: We have since had an appointment at a tax firm, where a tax consultant and a specialist lawyer for tax law participated in the discussion. There, without any ifs or buts, the correctness of our view was confirmed: Although my father is the civil law owner of my house, that does not play a role for the tax assessment. Here, civil law and tax law diverge. For tax purposes, the tax office attributes the house to me. This means: If the event of inheritance occurs, the house I live in is not subject to the assessment of inheritance tax. And for the rest (i.e., the land and the old house) the allowance applies. Only everything beyond that is subject to inheritance tax.
Whether we still transfer assets to me or my mother now will be examined more closely there, because other values also come into play. In any case, solely for reasons of avoiding inheritance tax, there is no reason to divide the land, which would also cause considerable costs. We disregard the aspect of the need for care because it is extremely unlikely that this would overstrain my parents’ financial capacity and would ultimately lead to recourse to my house.
From this point of view: Contrary to what is assumed here, there is actually no urgent need for action.