Your gerbils are females? Well, to tell you the honestly, female gerbils are harder to mix. They are territorial. Males are not as territorial as males.

There is a way but it will not 100% gonna make your gerbils like the new gerbils.

First, wash out Storm's and Dusty's tank with soapy water, dry it and replace with fresh shavings and hay. Do not put in their wooden toys or decorations in it. Then take the new gerbils and place in this cleaned tank. Later on add Storm and Dusty. Bound to see them fight. If they do fight in the tank, take all the gerbils out and place in a nuetral place like your bed or a table. This introduction process may take you a week...

Why fight? Gerbils live in colonies.... each colony is different, if you bring a new gerbil into a colony, fights will occur. Normally a colony only has 1 dominant female and 1 dominant male, the rest are the sons and daughters.

Male to male introduction is easier and it is even better if it's introducing a younger male to an older male.

Ok, back to females... if the introduction thru cleaned tank and nuetral place fails, then make a split cage. I do not have any pictures but you can find one if you search thru the net. You may need to DIY the divider. Anyway, just divide your tank into 2 sides, place your Storm and Dusty in 1 side and the new gerbils at the other side.... let them stay in this way for about a week, later you let them mingle in a nuetral place. If they still fight, let them got thru the split cage method for another 2 weeks... if it fails again, then I suggest you just let them have their own tanks and don't bother introducing them again.