Ther are two issues here, the seizures/EEG changes, and the developmental issues. They may be related or unrelated. The EEG reports sound very confusing with both focal and generalized features. To have the seizure issue sorted out I would suggest a consult with a pediatric epilepsy doctor or if one is not available an adult epilepsy doctor who is willing to see kids.
Regarding the developmental issue, it could be several things. The possibilities include mitochondrial disease, muscle disorders, or metabolic disorders to name a few. A muscle biopsy would be helpful in the evaluation, however it needs to be done properly and analyzed very careful.
My recommendation would be to make sure your child is being treated at a large academic center by a pediatric neurologist, and perhaps a pediatric epileptologist. If you are in the area with have an excellent department at the Cleveland Clinic.