Your parents should read the “Medicare primer” posts by @JohnT in this thread. I just went through the Medicare sign-up process and his clear explanation was a lifesaver. The thread is from 2021, so I wondered if rules might have changed, but as far as I call tell everything he wrote is still true.
You can’t just sign up any old time - for Medicare Advantage and the supplemental plans, there is an ordinary enrollment period (I think it is around October to December every year but don’t take my word for it). I am not sure how Medicare Part A (hospital coverage) will work for them since I think there is a 3-month window leading into your 65th birthday when you are supposed to sign up; obviously that has passed for them. But, there are SEP (Special Enrollment Periods) for people who need to sign up outside the usual periods - maybe they will qualify for one.
To figure out their enrollment period and what the best plan is for them, they can contact the SHIP in their state for help. Every state has one - it is a federally funded program to help people navigate the incredible confusion that is Medicare.
Finally, I note that JohnT’s advice includes this, and I don’t know how that will affect what is their best choice. But if I were them, I’d start researching this NOW:
· You are guaranteed to be issued a MS [Medicare Supplement] plan when you turn 65 (or first get Part B, whichever is later), but after this “guaranteed issue” period, you will have to pass medical underwriting to get a supplement plan, something difficult for many seniors to do.