Ciao Mauro. The title of this Beatles song came from a Jamaican Reggae band called "Jimmy Scott and his Obla Di Obla Da Band." The Beatles got copyright to use the band's title for their song. Paul McCartney, explained it "A fella who used to hang around the clubs used to say in a Jamaican accent, "Ob-la-di, ob-la-da, life goes on bra,". In this song the word "bra" is the Jamaican way of saying "bro" meaning brother.

I think it is another way to say "bro", which is short for "brother".He is referring to you, the listener, as brother

I had assumed it was made up to fit a rhyme! Songwriters have been known to do that. ;) If my experience is anything to go by, the average native English speaker wouldn't get the "bra=bro" reference and just giggle at the idea that it might mean "brassiere". Then keep singing along. ^^

That's my karaoke song but I didn't think about the meaning of the "oblada bra". But by the context of the song it seems that it means "brother" and it's practically a rhyme that's for sure. I didn't know "bra" is also a form of "bro" which most young english speaking people including Asians now.

No idea. Bra in America is a think that women wear to support their boobs. Also, in Black American English, 'bra' is a form of 'bro' which is short for 'brother' which is what many young Black people use as a greeting amongst themselves.