My Sim had twins in Sims 2 but they tended to float most of the time. Shortly after they were born I couldn't find one of them. Eventually got the other one up to a teen but still havent found the other twin. Her pic keeps getting red and I am able to refresh her so it is green again but still don't know where she is and can't control her or do anything to get her grown up. Afraid I'm just going to have to let her die and start over with another baby. Any suggestions ?

Move them out to a blank lot.

Do you have the bat box? Try 'Force errors - on in-world'

Also with the baby not being found, you don't have No Sim Loaded installed with out smarter EP check do you?
The mod requires the check to work, and without it you will get glitched births.

Came back to edit, realize i had left out an important word! 'NOT' lol.

If you had that particular combination of mods you would get constant glitches no matter what was happening, and if OP had had a glitched birth they would have gotten infinite babies until the game crashed. That's obviously not at all related to whatever happened here, that is in fact not always the problem whenever someone has an issue with the game

First time I installed No Sim Loaded I was playing a family due to give birth, I didn't have smarter EP check, I had a glitched birth, it happens.

Yes, it will glitch the birth if that's the first thing that happens in your game. You will get an error as soon as you load the game, regardless of what is happening, and in certain cases it will glitch a birth if that's the first thing that happens regardless of whether or not you have Smarter EP Check. Just because one particular thing happened to you does not mean that that exactly scenario always happens to everyone else. No one even mentioned any glitched births in this post, you just came in here with your wild superstition that everything that happens to you also is what is happening for everyone else.

It could be a corrupted hood like if you're playing the EA version of Pleasantview which is corrupted from the start or a glitch during birth caused an error with one baby and not the other.