It’s a family affair in more ways than one.

As a major mob racketeering trial gets under way today in Brooklyn, the blood ties will go beyond secret oaths and induction rituals — a Colombo-family soldier-turned-FBI informant may testify against his own brother.

Sebastiano “Sebby” Saracino is scheduled to take the stand against his brother, Dino “Little Dino” Saracino, 39, a current Colombo soldier.

Dino’s cousin, former Colombo captain Dino “Big Dino” Calabro, is another FBI informant on the lineup to testify against him.

Dino Saracino and Thomas “Tommy Shots” Gioeli, 59, the former acting street boss, go on trial in federal court today for crimes ranging from murder to witness intimidation.

Gioeli’s cousin, ex-Colombo associate Tommy McLaughlin, may also testify.