I installed World Adventures today. I even think I installed it correctly!
Before I installed WA I deleted all of the hacks. I then removed all of the package files.
I installed the game. Then I copied the resource.cfg to Program Files\Electronics Arts\The Sims 3 World Adventures. I also copied the d3dx9_31.dll file to TS3WA\Game\Bin.
I returned the .package files to their original place, but not the hacks.

I then tried to start the game. There seemed to be no problems; the game loaded just as quickly as it did before, I could still see my legacy family, so I selected them and entered their lot. In the lot everything seemed to be fine as well. There were no blue spots, the game didn't lag, all my sims were there and they seemed to be fine. Strangely enough two of my sims were standing IN their beds, and another was floating on top of his, but I didn't pay a lot of attention to that.

I then tried to select one of my sims and noticed something strang... The icons of their faces were no longer visible on the left side of the game! It was as if there weren't any sims in my house and if my sims were suddenly pretty ornaments I could no longer select and command. The game didn't freeze as I could still rotate and use the camera and move to different parts of the house. I've never had this kind of problem before or heard about it before...

So I entered build mode and tried moveobjects in order to place them somewhere else and then tried to enter the live sims mode. The sims live mode didn't crash my game, but it didn't load either.

So I left the game and once again removed the .package files and deleted the 4 cache files. I also deleted the already installed sims3packages. I've never installed a camera hack in my game. I once again tried to start the game, but the same problem I've mentioned before persists. My legacy house doesn't recognize its inhabitants anymore. They just stand in the house and won't do anything and I can't click on them and select them either.

Some necessary information:
Game version: 2.2.8.002002
I have a Hard copy of the game
System specs:
Acer - Intel Pentium 4 - 3 Ghz
2.0 GB RAM
Graphics card: NVIDIA GeForce 8600 GT
Windows XP

Is there a way I can save my family? Or do I have to uninstall both games and try again with a clean neighbourhood? I'd rather not lose my legacy.

Right off the bat, I can tell you that your computer doesn't meet the specs to run just the base game, much less the base game and an EP.

But, since you have removed everything custom, it's probably the game files. I would consider reinstalling (make sure to back up all your data). Then I would test with clean files to make sure that the game is working before adding anything back in.

Thank you for your help. I already suspected that my game couldn't be saved, but it still hurts. I've uninstalled the game and then I'll start all over again. If there's something wrong with my game I'd rather not risk adding any old data back to it.

I do still have one question though...
You stated that my "computer doesn't meet the specs to run just the base game, much less the base game and an EP".

I looked at the System requirements that have been mentioned on the DVD-case of WA. It says that the WA Requires:
PC - Windows XP, Vista or Windows 7
CPU - 2.0 Ghz P4 Processor or similar
RAM - (XP) 1 GB
VIDEO-RAM - 128 MB

I know that these are of course the minimum requirements, but I always thought I well met the requirements with my:
PC - Windows XP
CPU - 3.0 Ghz Pentium 4
RAM - 2 GB
Video-card - 512 MB

My game has always run like a dream, never lags, and loads in about a minute or two. What is wrong with my specs?

Mostly the processor. Not so good. But I don't think that is what your problem is in this case.

Did a reinstall help? It's a nasty surprise when you have to do that. I've been teetering on that abyss a few times lately!

I have no idea what the problem was, but the reinstall worked! I've even added a few hair packages and everything seems to be working smoothly.

Yay! Too bad it had to come down to a reinstall, but at least your game is working now. Well done.