Yes, the Sprint is an event. Think of it as a container event for the four other events you mentioned.
Yes, the Sprint Backlog will change during the Sprint - and it is changed by the Development Team - as the Development Team inspects progress made towards the Sprint Goal. The Development Team may renegotiate Product Backlog items with the Product Owner, as long as the Sprint Goal is not impacted.
There is no such thing as a Development Sprint. The Development Team's job is to deliver a "Done" Increment that meets the definition of "Done" each Sprint.