Albus didn't divulge that the barman of the Hog's Head was Aberforth, but he didn't deny it either. 

We do know Aberforth was in the Order of the Phoenix so they must have had a later cordial relationship, and Moody at least knew he was Dumbledore's brother, and had a thing for goats.

He also never hid the fact he had a sister, he just wasn't asked.

Harry, in _Harry Potter and the Deathly Hallows_, comes to the realisation that in all his meetings with Dumbledore he never once asked him about himself and his family, and as we only see Dumbledore through the eyes of the Harry we don't get to learn his past.

Aberforth blamed Albus for the death of their sister. That's why they fell out.