Those German machines are very interesting. Thanks for sharing. I haven't seen those combinations before.
The treadle cabinet that the Lotus machine is in does look like the Postwar treadle cabinets Singer sold in USA. My mother started teaching home ec in 1949 or 1950. They had one or two treadle machines in the home ec department at that time, and all students were required to learn how to operate one. It was still a rural area, and some old farmhouses had only minimal electric, mostly for lighting. Europe continued handcrank, treadle, and 3/4 size machines far longer than USA did.