Your funeral arrangements are a private matter. At least they are in my culture. If it is the same in yours rely on that convetion rather than try and explain to them why you think this will make you not-quite-dead. You don't need to be an evangelist about cryonics, when the subject does come up just state these are your wishes. If you opt for neuro preservation your relatives can still cremate the corpse and do with it as they please.

As to relationships, don't worry starting new relationships shouldn't be affected by this since its unlikely to come up. Perhaps just bring it up around the time oxytocin induced pair-bonding is peaking. "Love" helps people rationalize all sorts of stuff and later inertia and precedence should carry you through.