What you are describing doesn't sound like a typical seizure, although there are "partial" seizures that effect just one part of the body.
Partial seizures: Partial seizures are also called focal seizures and as the name indicates, the electrical storm is affecting only a part of the brain. A partial seizure may stay localized or it may expand to the whole brain and cause a tonic-clonic seizure. Because the seizure starts in only a part of the brain, an underlying disease or injury is highly suspected. A partial seizure may remain localized or spread to other parts of the cerebral cortex producing a sequential involvement of other body parts.
Partial seizures are classified as simple focal seizures when consciousness is preserved and as complex focal seizures when consciousness is altered. Any portion of the body may be involved during a focal seizure depending on the region of the brain affected. PARTIAL OR FOCAL SEIZURES
I would definitely get bile acids tests done on both puppies. They should be done on all non-symptomatic Yorkies at around six months since the incidence of liver shunts is so high in the breed. Dr. Center recommends symptomatic puppies be tested earlier. At 15 weeks they are old enough.
Let us know the lab results when you get them, okay?