in the meantime, apply for green card if they show any interest of staying with you, I've a friend, they applied for green card even their parents in china. but they hates live here, even twice a years, for a month.
They'll do just fine in flat if they choose to try first. or they can try to find a fine part time helper, come everyday a few hours, and find a person for them(your friend or your hu*****and's friend, their neibor) who can call on on emergency, pay money each time they help.
so many options, why just 1, you never know the answer, only if you try. older people are very hard to live with, but the most important is they are happy, feel cared about. if you sacrifice so much and they live miserable, what's for?