According to the Handbook of Applied Dog Behavior and Training, by Steven R. Lindsay, dogs can recognize their mothers, siblings, and even their breeders after several years of separation. Apparently, their highly developed sense of smell also includes a scent memory that helps them recognize their first “family” members.
I haven’t actually read the book but highlights of his book are posted on the internet. I’ve also read lots of anecdotal evidence which suggests dogs do and don’t recognize their mothers or siblings. So, I guess the answer is maybe.