Analyze the role of respectability in Tom Sawyer’s supposedly lawless gang. Why is it mandatory for each member to have a respectable family? Examine the idea that Huck, who has had more experience with breaking the law than any of the others, comes close to being excluded from the gang.
The "gang" that Tom Sawyer assembles swears an oath of loyalty. The oath promises that if a member of the gang gives away any secrets or tries to leave the gang, that member's family will be killed.
There is no mention of respectability in this section of the novel, however Tom does convince Huckleberry earlier to "go back to the widow and be respectable" as a criteria for joining the gang of robbers.
The simply explanation then for the criteria for joining the gang is one of collateral. Gang members must have a family to be killed in order to join the gang. When Huck suggests that Miss Watson can be killed on his behalf, the gang gladly accepts him.
Huck's family situation is indicative of the fact that his background is less "respectable" and less conventional than those the other boys. His father is mentioned as a person who is unreliable and of no account. Huck has no other family. While this means that Huck is perhaps more alone in the world, it does not equate to a statement on his morals. As the novel has already shown at this point, it is Tom Sawyer who acts on impulses that demonstrate a rather cruel indifference to the feelings of others.
"[Tom] is a foil to the practicality of Huck; he is the universal boy-leader in any small town who can sway his gang or his pal into any act of fancy, despite all grumbling and disbelief" (eNotes).
Tom plays a trick on Jim that is entirely unnecessary after being talked out of tying Jim to a tree. Huck takes no part in Tom's prank. So, if Huck is thought to have more experience breaking the law because his personal history has had him sleeping outdoors, smoking and moving from place to place, that history has not also made him an immoral person.
Importantly, the idea behind the gang is playful. The group decides to rob and kill as a matter of principle, but when one of their group begins to cry because he wants to go home, Tom gives him a nickle. This is not at all like robbery but more like a nearly polite bit of bribery. The group decides to ransom people who they kidnap, yet they cannot determine what it means to "ransom" someone.
The playful nature of the gang is ironic to some degree. In plotting evil, Tom shows that he can also be generous (sometimes). In creating a lawless group, the one member who has nothing to lose is almost denied entry.
We might reasonably or generally expect that the people with the least to lose would be the first members of a gang of lawless robbers, but with Tom Sawyer things always get complicated.