الحاج means someone who went "El Haj" To Mecca for religious purposes, is somehow used as a title to the person but for your information sometimes it is just used to call out for an old man just as you say mister or sir ( At least it's the case here in Tunisia) محمد المبروك is the full name of the man الله يرحمه : May Allah have mercy upon him ( it means that the man is dead) So no, it's not an expression and I think that it should have been a comma between المبروك and الله يرحمه

Yes it's just a Proper name !