I have only been able to find a source that claims some American architect's wife was his daughter. But I am really looking for any solid info (marriage certificates, birth certificates, newspaper articles) relating to his family life. I have looked pretty darn hard but my lack of german (or swiss-german) language skills might be letting me down.
I'm Swiss and just went through a lot of German websites but there's not much to be found.
Apparently he was married and had five daughters but I was only able to find out one name: Elsa Bosshart-Forrer. She was one of his daughters and married Swiss writer Jakob Bosshart.
You can see a photograph of him and his wife in this PDF which is also the source for the information above (together with this German Wikipedia page which says that Bosshart married one of Forrers daughters (Elsa)). It's the first big picture with four people sitting. Forrer is on the far right and his wife right next to him. The man and woman on the left were his guests but it's not said who exactly they were.
Besides this I've only seen one other PDF of a scanned old article from some magazine mentioning that he had a wife, but nothing specific.
*Edit because of correcting typos