I want to ask generally, do most U.S. universities offer on-campus accommodation for International Ph.D. students Who are married?
Probably not. Even when available, it might not be your best option. In some places on-campus housing can be a fair bit more expensive than renting from a private landlord. And if the university offers subsidized housing (whether on or away from the main campus) the waiting period can be quite long. Basically, you'd want to research your alternatives once you know where you might be going.
If the student is benefitted from scholarships {Free tuition and fees + 2k monthly stipend} will he/she need to pay an extra to use not-shared on-campus settlements?
Generally, housing wouldn't be free, but possibly subsidized.
Without any self-funding and other support, is the stipend enough to pay for it while taking care of food, health care, etc. at the same time?
It varies, so it's hard to say anything concretely. If the university pays for health insurance, that can be worth a lot actually. Also, living expenses vary considerably from place to place. I will say that if you have to pay for insurance yourself, and pay rent in a large popular city, well, money could be very tight.
Again, this is something you'll have to research when considering your offers. There are websites that help you compare these expenses between cities, to see if e.g. rent is particularly expensive somewhere.