If I understand your question, you are wanting to use an NCE Switch-8 stationary DCC decoder to power the tortoise switch machines shown in your diagram.
First the NCE manual for the switch-8 states:
Other technical stuff:
+We have successfully controlled two Tortoise switch machines with one decoder
output when used in a crossover. We can't guarantee this will work in all cases.
and
+The warranty is voided if the decoder is miswired, connected to more than 22 volts, or
used with switch motors drawing more than 40mA.
So... NCE will only guarantee it if each tortoise is connected to a separate output.
But they are saying that yes you could try to connect 1 and 4 to one output and 2 and 3 to another output. So, yes, what you propose will probably work and this is probably what I would do.
Theoretically one could connect all 4 turnouts to 1 output (since if one is crossed the other is unusable if straight), but that would probably draw too much current and damage the decoder. 4 X 15ma = 60ma
Does that answer the question, or at least help?