Arta Dracula is the brother of Count Dracula and Ivan Dracula. Not much is known about him since his existence was only revealed during the last half of Young Dracula Series 4 episode 4 'The Crown of Ludlaw Erant'.
He is (or was, they may be divorced) married to Elisabetta, who apparently had an affair with the Count.
He is the brother of the Count and whether or not he is younger or older is unknown. It appears that the Count is hiding what he knows about him.