Here are two more vanishing 12-plets similar to yours:
$$ \substack{ \displaystyle{◻◻◼◻◻◻} \cr \displaystyle{◻◻◻◼◻◻} \cr \displaystyle{◻◻◼◼◼◼} \cr \displaystyle{◼◼◼◼◻◻} \cr \displaystyle{◻◻◼◻◻◻} \cr \displaystyle{◻◻◻◼◻◻} } \quad \substack{ \displaystyle{◻◻◼◻◻◻} \cr \displaystyle{◻◻◻◼◻◻} \cr \displaystyle{◻◻◼◼◼◼} \cr \displaystyle{◼◼◼◼◻◻} \cr \displaystyle{◻◻◼◻◻◻} \cr \displaystyle{◻◻◼◻◻◻} } $$
I found these using JavaLifeSearch, combined with manual filtering of the search results to skip any non-polyplet patterns. I'm pretty sure that, together with your 9- and 12-plet and the 9- and 10-plets found by Noam D. Elkies, these (and their rotations and mirror images) are the only vanishing polyplets with 5 to 12 cells in Conway's Game of Life. That said, it's always possible that I've made some kind of a mistake in my search or filtering, so independent confirmation would be nice to have.
(It's perhaps worth noting that 1-step vanishing patterns in standard GoL (rule B3/S23) are exactly the same as still lifes in the "semi-complementary" alternative rule B3/S0145678, i.e. where the birth rules are the same, but live cells survive if and only if they would not survive in standard GoL. Thus, any existing software for exhaustively enumerating still lifes — or oscillators or spaceships, of which still lifes are a special case — in Life-like cellular automata could be used for this, at least as long as it doesn't have the standard GoL rules hardcoded.)
As for your bonus question, I'm not sure what you mean by "of an other kind", but it's pretty easy to use tools like JLS to construct large vanishing polyplets with arbitrarily complex boundaries and inner structure, like this somewhat whimsical example:
$$\substack{ \displaystyle{◼◻◼◼◻◻◼◼◻◼◼◻◻◼◼◻◻◼◼◻◼◼◻◻◼◼◻◼} \cr \displaystyle{◻◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◻} \cr \displaystyle{◼◼◻◼◻◼◼◻◻◻◼◼◻◼◼◼◼◻◼◼◼◼◼◻◻◼◼◼} \cr \displaystyle{◼◼◻◼◻◼◼◻◼◼◼◼◻◼◼◼◼◻◼◼◼◼◻◼◼◻◼◼} \cr \displaystyle{◻◼◻◻◻◼◼◻◻◻◼◼◻◼◼◼◼◻◼◼◼◼◻◼◼◻◼◻} \cr \displaystyle{◼◼◻◼◻◼◼◻◼◼◼◼◻◼◼◼◼◻◼◼◼◼◻◼◼◻◼◼} \cr \displaystyle{◼◼◻◼◻◼◼◻◻◻◼◼◼◻◻◻◼◼◻◻◻◼◼◻◻◼◼◼} \cr \displaystyle{◻◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◻} \cr \displaystyle{◼◻◼◼◻◻◼◼◻◼◼◻◻◼◼◻◻◼◼◻◼◼◻◻◼◼◻◼} }$$