How do you wire multiple outlets between three way switches?
First off, you CANNOT use #14 on a circuit wired with #12. If you do you'd have to replace the breaker with a 15A and this is simply foolish IMO. Why loose 5 potential circuit capacity amps over such an issue?

OK, you need to forget the physical orientation of the items. The fact that the receptacles are physically in between the switches is irrelevant.
You can wire it this way, but not with what you have and it gets complicated.

You should re-wire the receptacles with the proper 12/2 wire from one of the switches. Then use 12/3 between the two switches and feed the other switch. 
The only problem with this is that all three receptacles will be switched. This does NOT seem like a convenient setup, unless of course that is exactly what you want.

You can follow this wiring scheme shown as it is the easiest for DIYer and beginners, but remember that there is no one correct way to wire things. If you Google "3-way wiring" you'll find hundreds of diagrams people have drawn with just as many ways to wire.

Just think of your receptacles as the light in this diagram and continue on to the rest.