Perhaps:
Not entirely nuts
Going nuts

With a title like that it is more important to find an idiom that works in the target language than to translate the source literally.

You (naturally) don´t reveal in detail what the text is about, but unless the family also hit each other on the head, the Danish title is more interested in word-play than in direct relevance.

Translate the text, think about it as you go, and find an English expression that fits more or less.

Nutty as a fruitcake is probably NOT what you are looking for, but there are plenty of others.