I don't know anything about Sienna, but in regards to the questions about Excalibur, it's a new series, with Xavier and Genosha as the focal point. And it was kind of boring, hopefully it gets better, but they already spoiled it a little bit, with the appearance of.....can't tell, go read it yourself. It just kind of negated all of the importance of the last couple arcs.
Last time I saw them was right after Heroes Return, Quicksilver and Crystal, after defeating some witch girl in her middle ages fantasy land took a leave of absence from the team to spend time together. That was a couple years ago, and I skipped from that to Avengers #60 or so. So I don't know what's going on with them, other than the fact that Quicksilver adopted a newer and bad looking costume with stupid looking lapels. Wouldn't that slow the speed demon down, big 70's lapels aren't exactly aero-dynamic, and he hates being slowed down. His '97 era costume was the best. And I'm guessing Crystal is back up on the moon, cuz Mr. Fantastic teleported Franklin to the moon to have her babysit him a couple issues ago in Fantastic Four.
So far in Excalibur, the people we've encountered are, Xavier, Unus the Untouchable and 3 mutant friends of his, this girl named Wicked, a guy named Freakshow...and da-daa-daaaaa...someone else. Begins in M, ends in agneto.
I think it's supposed to be Zala Dane, and to keep anyone from guessing that the two might be linked, she went by Zaladane, instead of using 2 names or having a codename or something.
As for the other Quicksilver costume, I posted a pic. The Mutant X Quicksilver had a cool suit too, it was almost armor-ish (there was speculation that his atoms were flying apart because of his...fast paced life style)