First, it's within the division, I doubt that we would trade Marion to a team we play 4 times a year.
That issue tends to be exaggerated. Trades within a division don't often happen for the simple reason that it's more likely to find a trading partner in one of the other three (now five) divisions. But sometimes they happen and it's not a big deal. Also, the Suns play at least two games per year against everyone, so you're talking about a grand total of one or two extra games per season against a division opponent. Big deal.
Second, I don't think you trade the games best SF for 2 role players (Peja's a great shooter, but what else does he do? rebound? defend? pass?)
As others on this board have pointed out, Marion isn't a great SF anymore. He had a bounce-back season playing out of position at PF; when matchup considerations forced him back to SF, he struggled.
Stojakovic isn't a defender or rebounder, but Skinner is. Stojakovic also isn't much of a passer, but neither is Marion, so that's a wash. (Their career assist numbers are about the same.)
Plus in the limited time that I have watched Skinner he doesn't seem to fit the mold of what the Suns would need as a Center
I haven't watched Skinner much, so I can't debate this point one way or another. However, his reputation is that he is quite a good defender and rebounder. His career rebounds per minute (or per 48) are the same as Marion's, and he averaged almost nine a game after being traded last season, while still playing limited minutes.
If you want to do something with Q for Peja, I'm all ears.
There is absolutely no chance that the Kings will trade Stojakovic for a package headlined by Richardson.