I think my nieces deserve more.
what do you mean by your nieces deserve more?
I think my nieces are so nice, they deserve a lot of happiness.
It seems like you're pretty close to your nieces. It's great that you wish them good things.
My nieces have the potential to be a lot happier, I wish they had more.
Your good wishes towards your nieces is heartwarming, I hope they do get all the happiness they deserve.