soon to be single mother of both white and mixed-race chldren

I am a single mother of four children. My children and I all display strong Scandinavian traits (light, straight, fine blonde hair and pale blue eyes).

Seven months ago I was raped and as a result am expecting twin boys who will be half black. How do I make sure these children feel like they are part of this family? The chances of them looking much like their siblings are pretty slight. My older kids and I are completely accepting and are quite excited for the appearance of these two new little boys but I am concerned about how the boys may feel as they get older and the unwelcomed reactions of others who may make these six children uncomfortable.