I don’t think they realize the lobster is a criminal, or else they would be quite offended. I think at this point, they just accept his presence without really thinking about it. He can easily grab some cash while they’re discussing something else, and for some reason it’s just taken as a given that he has money. I imagine it’s how children manage to get into trouble even when their parents are generally vigilant.
If you wanted to read in to it, I imagine his larceny during conversation may stem from his communication frustrations, but I wouldn’t read too far in to it. The guy’s (lobster’s?) a jerk.