Hmmm...was pretty sure that both Tribunal and Oblivion Anniversary aren't Steam games - at least the retail disc versions of them aren't - or did he just download the games from Steam and put them on a disc for you?
If the NPC is actually wearing the Belt of Sanguine Fleetness, you won't be able to pickpocket it - you can only pickpocket items they aren't actually wearing. Also, just to discard the obvious - is your sneak icon displaying at the exact moment you pickpocket her?
Luck can also play a part - it's possible to have high skills and fail at something due to bad luck - which is why neglecting your luck skill isn't always a good idea, even though the skill may not seem to do much in everyday play.
I assume you're doing the Morag Tong questline - in which case you're expected to assassinate her in any case.
As for the two brothers - is it Navil Ienthith that you killed? Ranes isn't scripted to appear until after you attack his brother. If Ranes isn't appearing, you could try forcing via the console (if you've managed to get the console to work, that is!)
PlaceAtPC "Ranes Ienith",1,1,1
This should place him just in front of you. Or just type RA into the console to reset all actors back to where they're meant to be.
As for spells - are they not working at all, or just doing very little damage? Maybe you just need more powerful spells. You might need to do some new spellmaking
