sibling components

I've read the docs, and I just can't wrap my head around how to trigger a function in a sibling component.
Can anyone point to a reference that would explain it to a 5th grader? Thanks

Sibling-A has a list from a db
Sibling-B is able to remove a list item from db

I want Sibling-A to know that the item has been removed and re-render the list