About the Friendship Bug...
Like Tawmis said, I talked about it much earlier in this thread, so it's understandable that you'd have missed it. Fortunately, he provided the links. I can confirm that the Friendship Bug mod works, so it's definitely worth your while to download and install.
As of right now, there are four ways to fix or avoid the Friendship Bug:
1. Use the
Friendship Bug mod supplied on Dragon Age Nexus.
After you've downloaded it, simply place it in DA2's override folder. If you don't know where that is, it's found by going to "C:\Documents and Settings\[name]\My Documents\BioWare\Dragon Age 2\packages\core\override"
This is the easiest solution and probably the best one until BioWare produces a patch that fixes it.
I should also point out that this DOES NOT fix any speed or damage resistance issues already present. This mod merely prevents the speed modifier from subtracting from your overall attack speed, so if you've lost speed already, you need to use the editor to fix that first.
2. Deactivate Isabela and Sebastian's friendship bonus via the console editor. The console editor, despite the name, is only on the PC.
You need to first enable the console by making a shortcut on your desktop to the actual "DragonAge2.exe" and not the launcher, which is the normal shortcut. Right-click on the shortcut, choose properties and at the end of the Target field, add "-enabledeveloperconsole" without the quotes. Also, make sure there is ONE SPACE between "DragonAge2.exe" and "-enabledeveloperconsole" or it won't work.
By the time you're done, your shortcut's target line should look like the following: "C:\Program Files\Dragon Age II\bin_ship\DragonAge2.exe" -enabledeveloperconsole
Once that's done, start the game using that edited shortcut. While playing, press the tilde key (it's the one right above the left tab button) to access the console. Be careful when writing since you can't see the text you're entering. If you feel you've entered something incorrectly, just press enter and start over.
For Isabela: runscript removetalent 211040
For Sebastian: runscript removetalent 213050
That'll deactivate the "Thumbs Up!" and "Man of the Cloth" abilities from Isabela's Swashbuckler skill tree and Sebastian's Royal Archer skill tree. One note of warning, however. Whenever they level up, their friendship abilities turn back on, so after that you'll need to do this all over again.
If you're interested in doing more with the console editor, go to
this page on the DA Wiki. It'll provide you with everything you need.
3. You can avoid the Friendship bugs entirely by making Isabela and Sebastian Rivals. If you don't want to do that, then you'll have to make sure you only load a saved game with Isabela and Sebastian actively present in your party. If you do that, the bug won't occur. However, when you load a saved game without one or both in your party, the bug hits.
That means you can't load your game inside your house, for instance. You could, however, load your saved game in Merrill's house provided Isabela and Sebastian are, once again, actively in your party.
I think this is the toughest way to handle this bug, so I wouldn't recommend it.
4. The last thing you could do is use the DA save game editor. Just download the
GFF4Editor and click on "daosavegame.exe" within the editor's folders.
Click on FILE and then OPEN FILE. Find whichever saved game you want to edit and click on the actual file, not the folder it's in.
Once that saved game is open, click on PARTY to expand that tree and then click on your character's name. Find ID 32 for "Damage_Resistance" and ID 42 for "Animation_Speed_Modifier." You can't edit the base value, which should be "0.0" for both. The modifier value should be "0.0" unless something has either positively or negatively affected it.
In your case, the "Animation_Speed_Modifier" should read 5.0 (with Isabela's Friendship talent active), but the bug will have probably affected it. You could work around the bug by setting the modifier to "0.0" but I don't know if that fix remains permanent or not. You'd have to test it to be sure.
I don't know how the "Damage_Resistance" is modified by Sebastian's Friendship talent since I don't have the DLC with him in it.
Using this editor is the only way to fix already existing problems. This editor won't, however, prevent them from happening again. So it's best to use the editor to fix any problems you have right now and then do one of the three previously listed options in this post.