How do you come to that statement? Take a look at Wikipedia under Income distribution in Germany, there you can see where the "high earners" already start, with €75,000 you already belong to the upper 13.5% ....
But that doesn't help at all – he still belongs to the upper middle class. The top 10,000 are simply not the top 10%. The average people are all 95% or even 97.5% of the citizens in the statistics – after that, it gets interesting and really "big." And yes, I know the made-up boundaries sociologists draw regarding social classes – by the way, those are the ones who themselves say they know nothing about high earners and the upper class.
If he alone brings in €150,000, and his wife another €100,000, then he is slowly entering the entry-level class for "high earners." That way he has it comfortable, but by far not enough. If a completely normal 170 m² house of high standard, 5 years old, now costs around €1 million, unfortunately such an income is also not sufficient. So he can't be a high earner if the whole thing only runs on unrealized inheritance.
Then there remains the question whether the OP also has the power of attorney for care. Otherwise, there could still be problems with the seemingly secured inheritance.