Should anything happen

Regarding the following four sentences:

(A) Should anything happen, let us know immediately.
(B) Should something happen, let us know immediately.

(C) Should anything happen in my absence, ask her for help.
(D) Should something happen in my absence, ask her for help.

#1 Could you please evaluate each of the above sentences depending on whether it is natural?

#2 I think that in general, we should use "anything" rather than "something" in this kind of construction. What do you think?