I'm not actually deleting my Twitter acct for a couple reasons, significantly because that stops someone else from setting up with that username.
But when I occasionally double post, I do so manually, which I recommend.
But, importantly, if you're cross-posting then definitely don't boost people's posts there and seriously consider not RTing posts from there over here.
People will start blocking you if you don't. And that'll make this place less fun for you.