Basic obedience should not be a problem. You do not do any jumps or anything that should create a problem for either dog. Basically, they are learning to heal, sit, down, come when called, and stand for examination. I would not let the dog go above basic obedience though. The next level is jumping and drops on recall. I do not even recommend intermediate obedience for larger types of dogs until they are two years of age, regardless if they do not have joint problems. Their bones are still forming and growing and I don't like to take a chance in injury during this period.

If going from a stand to a down is too much then explain to the trainer that you prefer to go from a sit to a down and tell why. Any reasonable trainer will understand. Especially if you are not planning on competing. In my opinion, I believe the harder part would be getting the dog with displaysia to stand after being down.

The stand to a down is taught just to make sure the dog understands what down is. Sometimes things become routine and the dog will automatically assume "okay, I'm sitting. Next we do the down thing". Variety is the spice of life and the assurance your dog knows the commands!

As Carrie said, only you know what is best for your dog. When you see discomfort then you know I need to take it easy here.

One final thought. Walking is the best thing for displysia. Keep the dog limber and make sure you keep their weight under control. Excess weight is the hardest thing for the dog, especially when they have bad hips and elbows.

Have fun in training and let us know how it goes!