Hughes' family is very dear to him, but I think that's all too obvious by the extremes he goes to to show off his daughter (giant photo towering over all who gather to watch the battle between Roy and Ed, anyone?). In a series where happiness is a rare commodity, Hughes' loving family unit is a safe-haven for the Elric brothers, and the audience.
Gracia (グレイシア) is Hughes' wife, and one could easily get away with calling her Hughes' better half, if only because she's just the sweetest lady (no less than Hughes deserves! XD). Gracia's a full time housewife/mother, and fully supports her husband behind the scenes, even when she knows how dangerous the business he's involved in is. She also treats the Elric brothers as if they were family (and baked Ed a birthday cake!) and then extended the same kindness to Winry when Hughes brought her home with him. It's no wonder Hughes adores her!
Elicia (エリシア) is Hughes' daughter (who by the time of the current storyline is three years old), and he loves her to no end. Before she was even born he would brag about her ceaselessly, and he dotes on her something fierce now that she's out of the womb. Of course, he also gets a bit overprotective when young boys make advances to her, even if they are only three years old. But enough about Hughes, Elicia is a sweet and carefree girl; her young age and loving family make her blissfully unaware of the problems found in the world outside her home.
Roy is a very good friend of Hughes', as well as the Flame Alchemist and a Colonel in the military. Roy trusts him more than any other person, which is understandable, as Hughes supports him from below while Roy tries to climb to the top of the military. Hughes passes him information, often over the phone under the cover of bragging about his family to Roy. Granted, he sometimes phones Roy just to brag about his family anyways. And Hughes' support extends beyond the professional sphere, as Hughes was there for Roy after he returned from the Ishbal rebellion and was having trouble dealing with what he had done in the line of duty. Everyone needs a friend like Hughes!
ED and AL
As we've already established that Hughes is the nicest damn guy ever, it's not at all surprising that he acts like an uncle to the Elric brothers. He tries to look out for them and protect them, and teases them when the opportunity presents itself. Solidifying their near-family status, the brothers were even around for Elicia's birth. And I'm too lazy to draw their picture right now.
When Winry comes to visit the Elric brothers, they're currently hospitalized and in not much shape to play host to their friend, so she (unwillingly) becomes a guest of the Hughes family. And, like her childhood friends, is instantly taken into the family (almost like a sister to Elicia). Even after her brief stay comes to an end, she returns to the Hughes household to visit every once and a while.