When my son and I play, the one that signs on first can use his "Mii", the second player is simply "player 2". How can we both use our "Mii's"?

Sounds like a laser read problem
take back to retailer and get it replaced or repaired under warranty

It is under SONY warranty, please contact SONY, they will ship you a new one.

Click the shadow of a person with the + sign and choose a Mii from your Mii Plaza, you could only have up to eight Mii registered on wii Fit per Wii.

Discovered that whatever Mii you pick first has to be the one to open the advanced levels. It does save it under that person, but if the whole family is playing and you go back in and pick someone else first, then that person won't have the advanced levels until it is achieved.

We had the same problem. Removing the Mii from the Mii Channel kept a generic Mii character in Wii Fit so we still had a problem. After about 3 failed attempts at a password, Wii Fit will ask for a height verification. Start making guesses as to what the person's height is and eventually you will get access and from there you can get into their Profile in Wii Fit and delete them.

you might be using the second remote instead of the first

Rock Band is a 4 player game, each player taking their own role. They can choose from Guitar, Bass, Drums or Microphone. If your daughter wants to play guitar and sing at the same time, she will need to play a multiplayer game and use 2 Mii profiles, one for guitar and one for singing. 
A single player cannot play 2 instruments using the same Mii either. You must use separate profiles. 

yes actually your son changed your settings there is an option in there its called intro or somthing named like that what it will do is play the first 10-20 secends of a song and switch to another one and so on


~Temp

well it makes sence u should have waited okay u should go to your mii chanel and cheak can u help me with my wii problem

The songs are in the wrong format - use mp3 format files for best results