Happy New Year! I have a question or two about death.

I have a will, it says that everything goes to my sister (not that there is much). It also stipulates that my dog goes to my sister, but if she is not willing or able to take my dog, then it goes to my ex-wife.

If I become acutely aware of the amount of time I have left (like if I get cancer of the everything) then my intention is to give everything away and exit stage left without anything but the swim trunks they dump me into the sea with.

But my question is how does one create and enforce certain directives about one's death? Like how does one say they don't want a funeral or that they want their relatives to sit Shiva? How can I direct my next of kin to bury me at sea or cremate my remains?