Sorry to hear about your health. The 2nd option is a definite. No-No for getting visa. It's very unlikely that u will be granted US visa just because u want to see ur cousins.

Now regarding the first option of medical treatment, u should be able to get visa if you could provide following.
1. Medical assessment and referral from your doctors recomnending u to go to US for additional treatment
2. Medical cost coverage: Proof of your medical coverage while in US. If u dont have insurance or ur current insurance does not cover the costs in US, u have to provide the proof of financial support. For the type of treatment you are talking about, the medical bills will easily top several tens of thousands of dollars with no insurance. You have to first talk to the doctors in US who can provide u approximate cost of treatment. For visa interview, u have to show proof of support of those costs in addition to ur living costs during ur stay.