All the characters get along very well when they are alone like 99% of the time. It's such a great schtick that they end up going at each other again when the group is altogether. I'd say that Charlie doesn't really care to much about what the gang thinks of him most of the time though. He doesn't ever really seek the approval of anyone or change his ways for anyone so I'd say that the only reason he rips on Dee and doesn't stand up for her is because he thinks Dennis and Mac and Frank are funny when they make fun of her. Maybe Charlie would stick up for her if he thought it was a big deal but I think Charlie knows that Dee is strong enough to not get bothered by most of the jokes that are at her expense. That's why the gang has such a good relationship. They rip on each other all the time and for the most part it doesn't bother them. Honestly, in my opinion after watching the show hundreds of times I've found that the gang is actually ripping on each other just as much as Dee. She does seem to be the main target at the beginning of the show but every character has gone through just as much ridicule as Dee and they all move on and it's not worth trying to defend each other since they're still close friends at the end of the day everytime. Dennis tells Dee that he loves her. Charlie has admitted that he would want to have sex with Dee. Frank obviously cares about his daughter which is why he came onto the show and Mac is actually the character I would actually consider being the one that would actually be wishing he was standing up for Dee more (He doesn't because he wants Dennis to like him). The only relationship in the gang that isn't friendly is Frank's relationship with Mac.