need to buy medical insurance for visiting parents?

[XHW]

My parents came to visit us for 6 months, is it necessary to buy medical insurance? What if they extend their staying to 12 months? Both of them are yonger than 60 and basically in good health, other than having some health problems common to aged people, like stomach uncomfortability,high blood pressure etc. Will the medical insurance cover these chronical diseases? Can we find any doctor in Chinatown who is specialised in treating these diseases? Thanks for any input.