Littermates may go on to do SchH, It is the bloodlines show the trainability in the titles in this sense. (However these days (sadly) with the abundance of "paper titles" you need to be very careful in selection from some lines to be sure what you are getting) SchH is a sport that I personally believe can be done with a Service Dog but I do not advise novice/inexperienced trainers to attempt it with a Service Dog.
I am not as experienced as you and many others on this forum are, but I think it would be a truly unusual and rare individual dog who could be a success on the ScH field and also be a sucess as a service dog, i.e. Seeing eye dog or medical alert dog.
Would you also say that the same dog could function as a K9 or military patrol dog and then also do service dog work?
If so, would you know of any individual dogs that are doing both kinds of work?
Even with a really good trainer for both! I am assuming that you do say that they would need a different trainer for each? Or can a single trainer also train a single dog to do both types of work?
Just doesn't seem like a single dog could be suited to do both - sort of like a single human being being a top notch CEO of a major corporation and also an inner city councillor to disadvantaged youth or maybe a priest.
I think the the GSD as a breed can do all kinds of work, but an individual dog who can do both is truly an exceptional representative of our breed.
And if you are breeding whole litters in which the individual puppies could just go to different homes and be trained to do any type of the great variety of jobs - then you are to be applauded greatly.
And asked to pass along your secrets to other breeders as well.