Getting your parents to US is a double edge sword. While we (younger generation) can barely get used to live in the US, it will be very hard for them. Those 2 culture are on the opposite side of the pole. Many of the Nepali in the US can bring their parents just like you but choose not to cause they will die here out of boredom. There will be very few things they can do even if they were to drive around. Life without work is simply unimaginable. Depending upon the age and their willing to change, if they do get a regular job, it might work the best.
Not to discourage you, it is good that you want them to "try".
If you can elaborate on your place and the city, we probaly can add more ideas. Local churches will always have activities and volunteering job which can keep them busy. But if they're biased towards Christianity, then forget about it. Local library is a good place to hang out and read book or even work part time, look out for volunteering and charity works. I see lots of old Indians working at Goodwill, Salvation Army, etc
Depends on your life style. If you own a damn big property, hell, get them to garden. Make sure then get plenty of "walks" that will keep them healthy, they got all the time.