I'm new to the DishPro stuff, so I can't give you a definate answer. But I can tell you why it probably won't work. With the legacy switches, you can't mix two of the same switches. The LEGACY Twins have what is essentially a SW-42 in them, which is why they can be mixed with SW21s in the right combinations. But you can't use two twins, because then you essentially have two SW-42s in the mix.
I know this is at least somewhat true for DishPros, because I know you can not mix a DishProPLUS twin with a DP34. The DPP Twin basically has a DP34, only two of the outputs aren't there. You can't even use a DP21 with a DPP Twin, only a DP44.
I would imagine there are one or more reasons why this wouldn't work for you. The most important is probably using two Twins...two identical switches.
You might be able to put a DP Dual on one of your dishes for 61.5. This would be the most economical solution. But that depends on whether you can mix a DP Twin with a DP21.
There could be other factors as well. I'm finding out that my legacy setup that worked fine for 110/119/148 doesn't work for 110/119/129.
So, wait until you hear from someone with more DP experience, but I wouldn't get your hopes up.