I would just say to them when they say you offend them; “Really you don’t say, fancy that “. And leave it at that.

Oh dear As if god can’t take care of himself.

In the words of a certain wise man

There is no unseen, unknown function built into computers/iPhones that automatically activates when an atheist post is detected. It doesn't reach out of the screen or wherever to force anyone to view the content. Post away and realize that their reactions are irrelevant. They are, after all, irrational people who have no valid argument working for them.

Freedom of speech still applies even if your friends are bigots. Their feelings are not more important than your own and it may be time to reevaluate who deserves that "friend" title.

Post away, post away. If they don't like it, they don't have to look at it.