I'm glad you brought it forward into this thread because it's important.
For the most part, it seems that all/most of the legal players and expert witnesses here have known each other and have worked with each other, in some cases many for years.
It's what they do. It's their jobs. They're able to separate business from personal. When this trial is over, they'll work together, again. Heck, if SA trials are regularly televised from now on, we may get to know some of these people better ourselves.
All that being said, if I were a naive defense client and saw my lawyer chatting away happily and yucking it up with the opposing side, I'd really be upset.