So what are the incest options ?
Few scenes between related NPCs. For example, you can invite Zent's mom to stay at your Castle in ActIII and get 2 scenes between them, among other examples.
A lot of scenes between farm origin PC (Playable/Player's Character) of both sexes and his or her mother.
Several scenes between PC of any sex and origin and his or her sister.
Few scenes between noble origin malePC and his mother.
If you want a route that is rich of incest, try picking male sex and farm origin. It by far has the most incestous content. Mom scenes are quite numerous, easy to come by and most could be seen in early game.