Can I help by pointing out flaws in your implied argument ("I believe cryonics is worthwhile, but without my family, I'd rather die, and they don't want to")?

Do you intend to kill yourself when some or all of your current family dies? If living beyond them is positive value, then cryonics seems a good bet even if no current family member has signed up.

Also, your arguments to them that they should sign up gets a LOT stronger with your family if you're actually signed up and can help with the paperwork, insurance, and other practical barriers. In fact, some of your family might be willing to sign up if you set everything up for them, including paying, and they just have to sign.

In fact, cryonics as gift seems like a win all around. It's a wonderful signal: I love you so much I'll spend on your immortality. It gets more people signed up. It sidesteps most of the rationalization for non-action (it's too much paperwork, I don't know enough about what group to sign up, etc.).