What's the chance of a lecturer in foreign country to obtain a teaching job in US community college?
The safe thing to do is to assume, for the time being, that their stay in the U.S. should be minimalist, and that they should hold onto their existing jobs in their home country.  However, your mother could certainly apply for some teaching positions in the U.S., and if the job search goes well, your parents could change plans at that point.  (However, even in that case, I would advise them not to burn their bridges right away.)

Community college jobs do not necessarily pay very well, and there is no guarantee of getting such a position, for anyone, at any given time in any given location.