I think I will side with my nephew instead of my family during dinner.
Where does this wanting to side with your nephew come from?
I went through tough times with my family so I know how he feels.
Having a tough family life is difficult to deal with, but siding against part of your family to support your nephew creates conflict when everyone should be supported. Don't take sides in this matter.
I'm going to tell them the truth.
Family should want to support one another. If you take sides you create more conflict. You should try and be the mediator between them.