Lifting your nephew would be fine. I lifted my DS2 throughout my entire pregnancy with DD2 and I had no dramas and the same went for my older 2 children also.
I have moved a few times through pregnancies and basically I do the moving of the lighter boxes. I do also help with things like the dvd player, smaller TV's, computer, and some bits of the beds. I make sure whatever I am carrying isn't awkward nor too heavy.

All the best for your move hun