Tolkienites already know that they are brothers. Non book readers eyes glaze over at this kind of extra explanation, although a chief complaint was that I keep reading over and over was that 'the dwarves weren't interesting or differentiated enough.' However, I don't think family tree discussions would make much difference to those folks.

Rhyming names clues you that they are related. There's enough Thorin son of Thrain son of Thror to give you a clue that character with similar names might be at least distantly related.

The Fili/Kili/Thorin thing can be explained in a later film.

It's another book versus movie detail that often gets shorted when the footage is added up. There may well have been a couple of mentions, but how many lines are we talking about, four or five to cover the various brother groupings? I suppose it could have been done.

Is it essential? Maybe. It depends on whether you want people to care more about a specific character, and I think Fili/Kili will be explained a little more later.