Visitor Insurance

I am really confused about whether to take insurance or not for my parents who are coming in january.I cant figure out which insurance to choose.what is meant by pre-existing conditions.my dad has a back problem often.so if he has a backache etc is it covered?also shud i take a plan with a high deductible?does that mean that in case we take them to the doctors we have to pay the deductible anyway regardless of the cost incurred?also what is meant by maximum coverage for principal applicant as well aas spouse?and how much is the average medical cost that can be incureed out here?is a maximum coverage of 100K good enough?also if anybody has bought insurance and had some personal experience as to using them please let me know.thanks a lot
grace

If you read the some of the artiles arctiles given on this website, some of these things can be clear for you.
Once you undersnat these basic things then decide on what kind of plans suits for the visitor.