The question about costs did not come up :)
Nevertheless, it does not matter whether grandchild or nephew. It is not the degree of kinship that counts, but the number and closeness of the persons ;)
However, I am confused when I ask who the residents are supposed to be, then get the answer "me + my nephew," but then again the reference to "husband and me" (+ nephew).
There is indeed a difference between planning for a single household or a married couple.
Maybe one should not see the nephew as an individual, but as a family.
The day before yesterday, a bungalow for 2 people was requested, and a page later the son was mentioned, who regularly comes home on weekends.
Of course, everything can change, but both the original condition and later modes of existence should work.