I don't know Rose, maybe it is a crapshoot. My older natural sister and I look nothing alike, nor does my older natural brother. Older sis has blue eyes, red hair; older bro blue eyes and blond hair. My younger sister is my doppelganger however, except for height---I am short and she is tall (if I were only taller I would be thinner, LOL!) Our faces are exactly alike though, we could be twins, except she has blue eyes, I have hazel (but my eyes were dark brown until I was about 18 then they turned more green). She has more natural blond than I do I think, Miss Clairol helps me with my blond.
Ironically, I have a similar look to my adopted family, to the extent that when people would find out I was adopted, they were shocked. It made me feel good when I was growing up that I looked similar to them-helped me feel more like I belonged.
However, in this family, my brother and sister are quite obviously siblings, and they have very strong features of both my mom and dad and each other. Several of my cousins look very close to my brother and sister too--people who saw all of us would know that we are related. I really do think that more families share resemblances than not.