What is the norm in PhD internships in terms of their duration, tasks, and location.
For research internships I think doing a bit longer will result in better outcomes. In my experience it takes 1-2 month to get into a new work environment/topic and doing serious research in 2 month is unlikely.
The best way to find out is to talk to your supervisor (at the internship) about this. The internship should not be a pure engineering task (it is still a full-time position though). It is probably to be expected that you do some hands-on work but you can ask about the topic and the probability that this will result in a publication. Depending on what your PhD topic is, you could also see this as an opportunity to get some real-world experience.
This is quite normal (I moved to the US for 6 months, I know a lot of people who did this). Of course if you do not want to do this, your supervisor should not be pushing you. 


It would be best to consult with your advisor before searching for something else yourself. Maybe he just wants the additional funding for you but maybe there is something else about this internship that makes him think it is suitable for you.