Cas did hang with a gang until reasonably recently. DMS was the local gang boss and Ice and Cas were his trusted muscle. With DMS's brains and Ice and Cas as muscle they easily became the dominant local gang.
Cas recently split with DMS (and this Ice too).
Ice and Cas together with DMS's brain easily kept any threats down. Combined with the good will that he made by actually helping the local hood, ment that there were only a few threats to the turf (mostly from outside).
This all changed when DMS and Cas got freaky. Cas was always wary of emotional attachment and DMS was especially a danger (because he didnt use physical means to get what he wanted). Cas freaked out (terrorfied of the emotional attachment and also knowing that she would screw up DMS's life just like she always did with others) after so she ran.
Cas has no experiance with a relationship that works and can only really handle abusive or broken relationships and she feels threatened by emotional closeness (although she wants it and tries to find it, which just makes it all worse). DMS freaks her out the most because she expects violence to be part of a relationship, but she knows that he would never harm her.
She needed to make sure DMS didnt follow, so she burnt some bridges. Cas made her exit from DMS and the gang as public and humiliating as possible for DMS. She dumped out some information very useful to rivals and made it clear that she had a very low opinion of DMS.
After Cas' exit, DMS and Ice had their hands full keeping the gang and the hood in order. There were some mumbles from below about challanging DMS for leadership and rival gangs started encroaching on their turf.
DMS and Ice had the most trouble from Will "King" Stone who runs the Shadows (a rival gang). King was a member of the Snakes before DMS took over and was just about to challange for leadership when DMS took advantage of King's weakening of the previous leader and took over. King was forced out and started a rival gang nearby with those people that DMS' "warm fuzzy" leadership pushed out (IE, those who wanted to bully power and cash out of people). King considers the Snakes to be his gang on his turf and just drools over any chance to take control.
Some of the gang who thought that she was a "cavebitch who didnt belong" sought her out for some "revenge" and she left them bloody and broken. This didnt make DMS's life any easier.
This may threaten TF and Sarah now that Cas has 'gone' (with Renee and the gang).
Sarah is very quiet and damaged thanks to some horrible event in her past and neither Cas or TF had got to the bottom of that. Like them, she is a runaway with a past that noone talks about.
Sarah is very thankful to Cas and TF because the provide a place to live and security. Plus, home feels a little like family for all of them (well what they think family is).
Neither Sarah or TF want to become involved in the gang, so they try and stay distant, but the gang runs the hood and DMS is the leader, so they cant avoid it (although Cas used to insulate them somewhat).
Ice likes them both and will make sure they are OK now that Cas has dissapeared (with Renee etc).
DMS would care for Sarah out of his sense of brotherhood. TF also, although he doesnt like the fact that TF is so StarWars obsessed (as thats white propaganda see the talk at the start of "Chasing Amy" :). DMS also knows that TF is a little disturbed and weird. They just dont get along.
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When the Renee stuff started, she came back and left him with a $50. If he is really hard pressed, he might ask Lucy for some food.
Sarah hardly goes outside (it scares her). She looks after the house for Cas and TF and in return gets food and a bed.