Honestly? If you have those games for the PS2, I wouldn't buy the Wii version unless the kids are still playing them quite often.
HSM is a singing game. I think the girls might have fun with that one for a while.
By 'Game Party' do you mean Mario Party? I would suggest that one too.
Here's my list in order of importance for those ages (excluding GH and DDR).
1. Super Mario Galaxy
2. Wii Play (for the second controller)
3. Zelda
4. Rayman
5. HSM
What other games do they really like for the PS2? That will help me give you better suggestions!
Yes, there definitely will be a shortage. In fact there is one still right now. There have not been enough systems to keep up with the demand since it came out and it will get really bad again soon. But I still would not buy a bundle that has stuff I don't want until the beginning of November. I've seen and heard about enough systems available at local stores to not get panicked yet.