In v2.6 you can't control the order, the elements are handled in the order in which they're stored in the collection inside the entity (EntityDefinition.Relations), so the order in which they're deserialized is the one they're handled in.
Which is every time the same btw (2.6 was the last version which used the binary format so uses binary serialization), but there's no ordering applied so there's no guarantee the order is the same.
If you want an ordering there, you can alter the code generator sourcecode btw, it's in the SDK archive on the website: log into the site with your customerid+pwd and go to My Account -> Downloads -> 2.6 -> Extras. There you'll find the SDK which contains all sourcecode for e.g. runtime, code generators etc. Go to TDLInterpreter\Interpreter.cs, line 3101 and apply ordering there.
The code is over 10 years old so it might look a little ... old fashioned