From a role-playing perspective we are not. History has demonstrated that pretending to have a family of players within Wessex ultimately creates excessive drama through various causes. I know I am being vague, but those stories can be found in various areas of the forums.
For real life relatives, absolutely. You would not be the only member to have family in the guild. Some choose to have same the last name and act as family in the game. Others play as strangers, or simply comrades with a long history between them.