Everytime I start a new household my other Sims are not there

Could you try loading another save file? Sounds like your game made a new file to start in.

I did and the same thing happened. I've got 4 families and not all of them are in the same 'world'. 

Two families are in the City but on each saved file , I've only got one family in the city.

It is part of the game! All of the Sims that you don't make are basically the starter Sims. This means in every world you have, the Goths will be alive, until they die again.

OK, but it doesn't explain what's going on with my households. I used to be able to visit families I previously made and now I can't,

Only one family per world.

So what you're saying is that your save file split up in to multiple save files?

I think that's whats happened. I've never had this problem before.

That's weird. Did you try loading a fairly old one? 

I've loaded an old saved file and have 2 families in Newcrest, one in Oasis Springs and one in Willow Creek.

So don't know what's going on.

Is that save by any chance a good save or way too far back? 

I made the save file in Nove,ber/Decemeber. It's good, but I was planning on deleting it, but haven't yet.