I find myself often winging it with “themself/themselves” and it seems to be like themselves is always colloquially correct when there are multiple preceding nouns you’re referring to…
Otherwise if there’s only one antecedent or whatever, its themself
Be gentle haha
Farther/further
That’s just US vs British English. The US version being slightly more straightforward as is often the case.
Lol. Gets murkier when you’re in neither of those places and use a combo of both. I’ll stick with “closer” for now